IMAP Extensions: Quick Flag Changes Resynchronization (CONDSTORE) and Quick Mailbox Resynchronization (QRESYNC)

An IMAP server that supports CONDSTORE MUST associate a positive unsigned 63-bit (*) value, called a mod-sequence, with every IMAP message. This is an opaque value updated by the server whenever a metadata item is modified. The server MUST guarantee that each STORE command performed on the same mailbox (including simultaneous stores to different metadata items from different connections) will get a different mod-sequence value. Also, for any two successful STORE operations performed in the same session on the same mailbox, the mod-sequence of the second completed operation MUST be greater than the mod-sequence of the first completed operation. Note that the latter rule disallows the direct use of the system clock as a mod-sequence because if system time changes (e.g., an NTP client adjusting the time), the next generated value might be less than the previous one. (*) Note: RFC 4551 defined mod-sequences as unsigned 64-bit values. In order to make implementations on various platforms (such as Java) easier, this version of the document redefines them as unsigned 63-bit values. These rules allow a client to list all metadata changes since a well-known point in time, as well as to perform conditional metadata modifications based on an assumption that the metadata state hasn't changed for a particular message. In particular, mod-sequences allow a client that supports the CONDSTORE extension to determine if a message metadata has changed since some known moment. Whenever the state of a flag changes (i.e., the flag is added where previously it wasn't set, or the flag is removed where previously it was set), the value of the modification sequence for the message MUST be updated. Setting a flag that is already set, or clearing a flag that is not set, SHOULD NOT change the mod-sequence. When a message is appended to a mailbox (via the IMAP APPEND command, COPY to the mailbox, or using an external mechanism), the server generates a new modification sequence that is higher than the highest modification sequence of all messages in the mailbox and assigns it to the appended message. The server MAY store separate (per-message) modification sequence values for different metadata items. If the server does so, per-message mod-sequence is the highest mod-sequence of all metadata items accessible to the currently logged-in user for the specified message. The server that supports CONDSTORE is not required to be able to store mod-sequences for every available mailbox. describes how the server may act if a particular mailbox doesn't support the persistent storage of mod-sequences. CONDSTORE makes the following changes to the IMAP4 protocol: adds the UNCHANGEDSINCE STORE modifier. adds the MODIFIED response code that is used with an OK response to the STORE command. (It can also be used in a NO response.) adds a new MODSEQ message data item for use with the FETCH command. adds the CHANGEDSINCE FETCH modifier. adds a new MODSEQ search criterion. extends the syntax of untagged SEARCH and ESEARCH responses to include mod-sequence. adds new OK untagged responses (HIGHESTMODSEQ and NOMODSEQ) for the SELECT and EXAMINE commands. defines an additional CONDSTORE parameter to SELECT/EXAMINE commands. adds the HIGHESTMODSEQ status data item to the STATUS command. A client supporting the CONDSTORE extension indicates its willingness to receive mod-sequence updates in all untagged FETCH responses by issuing one of the following, which are called "CONDSTORE enabling commands": a SELECT or EXAMINE command with the CONDSTORE parameter, a STATUS (HIGHESTMODSEQ) command, a FETCH or SEARCH command that includes the MODSEQ message data item, a FETCH command with the CHANGEDSINCE modifier, a STORE command with the UNCHANGEDSINCE modifier, or an ENABLE command containing "CONDSTORE" as one of the parameters. (This option only applies when the client is communicating with a server that also implements the ENABLE extension .) Once a client issues a CONDSTORE enabling command, it has announced itself as a "CONDSTORE-aware client". The server MUST then include mod-sequence data in all subsequent untagged FETCH responses (until the connection is closed), whether they were caused by a regular STORE, a STORE with an UNCHANGEDSINCE modifier, or an external agent. A future extension to this document may extend the list of CONDSTORE enabling commands. A first CONDSTORE enabling command executed in the session with a mailbox selected MUST cause the server to return HIGHESTMODSEQ () for the mailbox (if any is selected), unless the server has sent a NOMODSEQ () response code when the currently selected mailbox was selected.

The Conditional STORE extension is present in any IMAP4 implementation that returns "CONDSTORE" as one of the supported capabilities in the CAPABILITY command response.

This document adds two new response codes: HIGHESTMODSEQ and NOMODSEQ. One of these two response codes MUST be returned in an OK untagged response for any successful SELECT/EXAMINE command issued after a CONDSTORE enabling command. When opening a mailbox, the server must check if the mailbox supports the persistent storage of mod-sequences. If the mailbox supports the persistent storage of mod-sequences and the mailbox open operation succeeds, the server MUST send an OK untagged response, including the HIGHESTMODSEQ response code. If the persistent storage for the mailbox is not supported, the server MUST send an OK untagged response, including the NOMODSEQ response code instead.

This document adds a new response code that is returned in an OK untagged response for the SELECT and EXAMINE commands. Once a CONDSTORE enabling command is issued, a server supporting the persistent storage of mod-sequences for the mailbox MUST send an OK untagged response, including the HIGHESTMODSEQ response code with every successful SELECT or EXAMINE command: OK [HIGHESTMODSEQ <mod-sequence-value>] where <mod-sequence-value> is the highest mod-sequence value of all messages in the mailbox. When the server changes UIDVALIDITY for a mailbox, it doesn't have to keep the same HIGHESTMODSEQ for the mailbox. Note that some existing CONDSTORE servers don't start tracking mod-sequences or don't report them until after a CONDSTORE enabling command is issued. Because of that, a client wishing to receive HIGHESTMODSEQ/NOMODSEQ information must first send a CONDSTORE enabling command, for example, by using SELECT/EXAMINE with the CONDSTORE parameter (see ). A disconnected client can use the value of HIGHESTMODSEQ to check if it has to refetch metadata from the server. If the UIDVALIDITY value has changed for the selected mailbox, the client MUST delete the cached value of HIGHESTMODSEQ. If UIDVALIDITY for the mailbox is the same, and if the HIGHESTMODSEQ value stored in the client's cache is less than the value returned by the server, then some metadata items on the server have changed since the last synchronization, and the client needs to update its cache. The client MAY use SEARCH MODSEQ () to find out exactly which metadata items have changed. Alternatively, the client MAY issue FETCH with the CHANGEDSINCE modifier () in order to fetch data for all messages that have metadata items changed since some known modification sequence.

C: A142 SELECT INBOX S: * 172 EXISTS S: * 1 RECENT S: * OK [UNSEEN 12] Message 12 is first unseen S: * OK [UIDVALIDITY 3857529045] UIDs valid S: * OK [UIDNEXT 4392] Predicted next UID S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited S: * OK [HIGHESTMODSEQ 715194045007] S: A142 OK [READ-WRITE] SELECT completed

Once a CONDSTORE enabling command is issued, a server that doesn't support the persistent storage of mod-sequences for the mailbox MUST send an OK untagged response, including the NOMODSEQ response code with every successful SELECT or EXAMINE command. Note that some existing CONDSTORE servers don't return NOMODSEQ until after a CONDSTORE enabling command is issued. Because of that, a client wishing to receive HIGHESTMODSEQ/NOMODSEQ information must first send a CONDSTORE enabling command, for example, by using SELECT/EXAMINE with the CONDSTORE parameter (see ). A server that returned the NOMODSEQ response code for a mailbox MUST reject (with a tagged BAD response) any of the following commands while the mailbox remains selected: a FETCH command with the CHANGEDSINCE modifier, a FETCH or SEARCH command that includes the MODSEQ message data item, or a STORE command with the UNCHANGEDSINCE modifier.

C: A142 SELECT INBOX S: * 172 EXISTS S: * 1 RECENT S: * OK [UNSEEN 12] Message 12 is first unseen S: * OK [UIDVALIDITY 3857529045] UIDs valid S: * OK [UIDNEXT 4392] Predicted next UID S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited S: * OK [NOMODSEQ] Sorry, this mailbox format doesn't support modsequences S: A142 OK [READ-WRITE] SELECT completed

This document defines the following STORE modifier (see Section 2.5 of ): For each message specified in the message set, the server performs the following. If the mod-sequence of every metadata item of the message affected by the STORE/UID STORE is equal to or less than the specified UNCHANGEDSINCE value, then the requested operation (as described by the message data item) is performed. If the operation is successful, the server MUST update the mod-sequence attribute of the message. An untagged FETCH response MUST be sent, even if the .SILENT suffix is specified, and the response MUST include the MODSEQ message data item. This is required to update the client's cache with the correct mod-sequence values. See for more details. However, if the mod-sequence of any metadata item of the message is greater than the specified UNCHANGEDSINCE value, then the requested operation MUST NOT be performed. In this case, the mod-sequence attribute of the message is not updated, and the message number (or unique identifier in the case of the UID STORE command) is added to the list of messages that failed the UNCHANGEDSINCE test. When the server finishes performing the operation on all the messages in the message set, it checks for a non-empty list of messages that failed the UNCHANGEDSINCE test. If this list is non-empty, the server MUST return in the tagged response a MODIFIED response code. The MODIFIED response code includes the message set (for STORE) or set of UIDs (for UID STORE) of all messages that failed the UNCHANGEDSINCE test.

All messages pass the UNCHANGEDSINCE test. C: a103 UID STORE 6,4,8 (UNCHANGEDSINCE 12121230045) +FLAGS.SILENT (\Deleted) S: * 1 FETCH (UID 4 MODSEQ (12121231000)) S: * 2 FETCH (UID 6 MODSEQ (12121230852)) S: * 4 FETCH (UID 8 MODSEQ (12121230956)) S: a103 OK Conditional Store completed

C: a104 STORE * (UNCHANGEDSINCE 12121230045) +FLAGS.SILENT (\Deleted $Processed) S: * 50 FETCH (MODSEQ (12111230047)) S: a104 OK Store (conditional) completed

C: c101 STORE 50 (UNCHANGEDSINCE 12121230045) -FLAGS.SILENT (\Deleted) S: * OK [HIGHESTMODSEQ 12111230047] S: * 50 FETCH (MODSEQ (12111230048)) S: c101 OK Store (conditional) completed The HIGHESTMODSEQ response code was sent by the server presumably because this was the first CONDSTORE enabling command.

The failure of the conditional STORE operation for any particular message or messages (7 in this example) does not stop the server from finding all messages that fail the UNCHANGEDSINCE test. All such messages are returned in the MODIFIED response code. C: d105 STORE 7,5,9 (UNCHANGEDSINCE 320162338) +FLAGS.SILENT (\Deleted) S: * 5 FETCH (MODSEQ (320162350)) S: d105 OK [MODIFIED 7,9] Conditional STORE failed

Same as above, but the server follows the SHOULD recommendation in Section 6.4.6 of . C: d105 STORE 7,5,9 (UNCHANGEDSINCE 320162338) +FLAGS.SILENT (\Deleted) S: * 7 FETCH (MODSEQ (320162342) FLAGS (\Seen \Deleted)) S: * 5 FETCH (MODSEQ (320162350)) S: * 9 FETCH (MODSEQ (320162349) FLAGS (\Answered)) S: d105 OK [MODIFIED 7,9] Conditional STORE failed Use of UNCHANGEDSINCE with a modification sequence of 0 always fails if the metadata item exists. A system flag MUST always be considered existent, whether it was set or not.

C: a102 STORE 12 (UNCHANGEDSINCE 0) +FLAGS.SILENT ($MDNSent) S: a102 OK [MODIFIED 12] Conditional STORE failed The client has tested the presence of the $MDNSent user-defined keyword. Note: A client trying to make an atomic change to the state of a particular metadata item (or a set of metadata items) MUST be prepared to deal with the case when the server returns the MODIFIED response code if the state of the metadata item being watched hasn't changed (but the state of some other metadata item has). This is necessary because some servers don't store separate mod-sequences for different metadata items. However, a server implementation SHOULD avoid generating spurious MODIFIED responses for +FLAGS/-FLAGS STORE operations, even when the server stores a single mod-sequence per message. describes how this can be achieved. Unless the server has included an unsolicited FETCH to update the client's knowledge about messages that have failed the UNCHANGEDSINCE test, upon receipt of the MODIFIED response code, the client SHOULD try to figure out if the required metadata items have indeed changed by issuing the FETCH or NOOP command. It is RECOMMENDED that the server avoids the need for the client to do that by sending an unsolicited FETCH response (see Examples 9 and 10). If the required metadata items haven't changed, the client SHOULD retry the command with the new mod-sequence. The client needs to allow for a reasonable number of retries (at least 2).

In the example below, the server returns the MODIFIED response code without sending information describing why the STORE UNCHANGEDSINCE operation has failed. C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) +FLAGS.SILENT ($Processed) S: * 100 FETCH (MODSEQ (303181230852)) S: * 102 FETCH (MODSEQ (303181230852)) ... S: * 150 FETCH (MODSEQ (303181230852)) S: a106 OK [MODIFIED 101] Conditional STORE failed The flag $Processed was set on the message 101... C: a107 NOOP S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed)) S: a107 OK Or, the flag hasn't changed, but another has (note that this server behavior is discouraged. Server implementers should also see )...

C: b107 NOOP S: * 101 FETCH (MODSEQ (303011130956) FLAGS (\Deleted \Answered)) S: b107 OK ...and the client retries the operation for the message 101 with the updated UNCHANGEDSINCE value. C: b108 STORE 101 (UNCHANGEDSINCE 303011130956) +FLAGS.SILENT ($Processed) S: * 101 FETCH (MODSEQ (303181230852)) S: b108 OK Conditional Store completed

Same as above, but the server avoids the need for the client to poll for changes. The flag $Processed was set on the message 101 by another client... C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) +FLAGS.SILENT ($Processed) S: * 100 FETCH (MODSEQ (303181230852)) S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed)) S: * 102 FETCH (MODSEQ (303181230852)) ... S: * 150 FETCH (MODSEQ (303181230852)) S: a106 OK [MODIFIED 101] Conditional STORE failed Or, the flag hasn't changed, but another has (note that this server behavior is discouraged. Server implementers should also see )...

C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) +FLAGS.SILENT ($Processed) S: * 100 FETCH (MODSEQ (303181230852)) S: * 101 FETCH (MODSEQ (303011130956) FLAGS (\Deleted \Answered)) S: * 102 FETCH (MODSEQ (303181230852)) ... S: * 150 FETCH (MODSEQ (303181230852)) S: a106 OK [MODIFIED 101] Conditional STORE failed ...and the client retries the operation for the message 101 with the updated UNCHANGEDSINCE value. C: b108 STORE 101 (UNCHANGEDSINCE 303011130956) +FLAGS.SILENT ($Processed) S: * 101 FETCH (MODSEQ (303181230852)) S: b108 OK Conditional Store completed Or, the flag hasn't changed, but another has (nice server behavior. Server implementers should also see )...

C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) +FLAGS.SILENT ($Processed) S: * 100 FETCH (MODSEQ (303181230852)) S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed \Deleted \Answered)) S: * 102 FETCH (MODSEQ (303181230852)) ... S: * 150 FETCH (MODSEQ (303181230852)) S: a106 OK Conditional STORE completed

The following example is based on the example from Section 4.2.3 of and demonstrates that the MODIFIED response code MAY also be returned in the tagged NO response. The client tries to conditionally STORE flags on a mixture of expunged and non-expunged messages; one message fails the UNCHANGEDSINCE test. C: B001 STORE 1:7 (UNCHANGEDSINCE 320172338) +FLAGS (\SEEN) S: * 1 FETCH (MODSEQ (320172342) FLAGS (\SEEN)) S: * 3 FETCH (MODSEQ (320172342) FLAGS (\SEEN)) S: B001 NO [MODIFIED 2] Some of the messages no longer exist. C: B002 NOOP S: * 4 EXPUNGE S: * 4 EXPUNGE S: * 4 EXPUNGE S: * 4 EXPUNGE S: * 2 FETCH (MODSEQ (320172340) FLAGS (\Deleted \Answered)) S: B002 OK NOOP Completed. By receiving FETCH responses for messages 1 and 3, and EXPUNGE responses that indicate that messages 4 through 7 have been expunged, the client retries the operation only for message 2. The updated UNCHANGEDSINCE value is used. C: b003 STORE 2 (UNCHANGEDSINCE 320172340) +FLAGS (\Seen) S: * 2 FETCH (MODSEQ (320180050) FLAGS (\SEEN \Flagged)) S: b003 OK Conditional Store completed Note: If a message is specified multiple times in the message set, and the server doesn't internally eliminate duplicates from the message set, it MUST NOT fail the conditional STORE operation for the second (or subsequent) occurrence of the message if the operation completed successfully for the first occurrence. For example, if the client specifies: e105 STORE 7,3:9 (UNCHANGEDSINCE 12121230045) +FLAGS.SILENT (\Deleted) the server must not fail the operation for message 7 as part of processing "3:9" if it succeeded when message 7 was processed the first time. As specified in , once the client specifies the UNCHANGEDSINCE modifier in a STORE command, the server starts including the MODSEQ FETCH response data items in all subsequent unsolicited FETCH responses. This document also changes the behavior of the server when it has performed a STORE or UID STORE command and the UNCHANGEDSINCE modifier is not specified. If the operation is successful for a message, the server MUST update the mod-sequence attribute of the message. The server is REQUIRED to include the mod-sequence value whenever it decides to send the unsolicited FETCH response to all CONDSTORE-aware clients that have opened the mailbox containing the message. Server implementers should also see for additional quality of implementation issues related to the STORE command.

This document defines the following FETCH modifier (see Section 2.4 of ): The CHANGEDSINCE FETCH modifier allows the client to further subset the list of messages described by the sequence set. The information described by message data items is only returned for messages that have a mod-sequence bigger than <mod-sequence>. When the CHANGEDSINCE FETCH modifier is specified, it implicitly adds the MODSEQ FETCH message data item ().

C: s100 UID FETCH 1:* (FLAGS) (CHANGEDSINCE 12345) S: * 1 FETCH (UID 4 MODSEQ (65402) FLAGS (\Seen)) S: * 2 FETCH (UID 6 MODSEQ (75403) FLAGS (\Deleted)) S: * 4 FETCH (UID 8 MODSEQ (29738) FLAGS ($NoJunk $AutoJunk $MDNSent)) S: s100 OK FETCH completed

CONDSTORE adds a MODSEQ message data item to the FETCH command. The MODSEQ message data item allows clients to retrieve mod-sequence values for a range of messages in the currently selected mailbox. As specified in , once the client has specified the MODSEQ message data item in a FETCH request, the server starts including the MODSEQ FETCH response data items in all subsequent unsolicited FETCH responses. The MODSEQ message data item causes the server to return MODSEQ FETCH response data items. MODSEQ response data items contain per-message mod-sequences. The MODSEQ response data item is returned if the client issued FETCH with the MODSEQ message data item. It also allows the server to notify the client about mod-sequence changes caused by conditional STOREs () and/or changes caused by external sources.

C: a FETCH 1:3 (MODSEQ) S: * 1 FETCH (MODSEQ (624140003)) S: * 2 FETCH (MODSEQ (624140007)) S: * 3 FETCH (MODSEQ (624140005)) S: a OK Fetch complete In this example, the client requests per-message mod-sequences for a set of messages. Servers that only support the CONDSTORE extension (and not QRESYNC) SHOULD comply with requirements from . When a flag for a message is modified in a different session, the server sends an unsolicited FETCH response containing the mod-sequence for the message, as demonstrated in Example 14. Note that when the server also supports the QRESYNC extension () and a CONDSTORE enabling command has been issued, all FETCH responses in Example 14 must also include UID FETCH items as prescribed by .

(Session 1, authenticated as the user "alex".) The user adds a shared flag \Deleted: C: A142 SELECT INBOX ... S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) S: * OK [PERMANENTFLAGS (\Answered \Deleted \Seen \*)] Limited ... C: A160 STORE 7 +FLAGS.SILENT (\Deleted) S: * 7 FETCH (MODSEQ (2121231000)) S: A160 OK Store completed (Session 2, also authenticated as the user "alex".) Any changes to flags are always reported to all sessions authenticated as the same user as in session 1. C: C180 NOOP S: * 7 FETCH (FLAGS (\Deleted \Answered) MODSEQ (12121231000)) S: C180 OK Noop completed (Session 3, authenticated as the user "andrew".) As \Deleted is a shared flag, changes in session 1 are also reported in session 3: C: D210 NOOP S: * 7 FETCH (FLAGS (\Deleted \Answered) MODSEQ (12121231000)) S: D210 OK Noop completed The user modifies a private flag, \Seen, in session 1... C: A240 STORE 7 +FLAGS.SILENT (\Seen) S: * 7 FETCH (MODSEQ (12121231777)) S: A240 OK Store completed ...which is only reported in session 2... C: C270 NOOP S: * 7 FETCH (FLAGS (\Deleted \Answered \Seen) MODSEQ (12121231777)) S: C270 OK Noop completed ...but not in session 3. C: D300 NOOP S: D300 OK Noop completed And, finally, the user removes flags \Answered (shared) and \Seen (private) in session 1. C: A330 STORE 7 -FLAGS.SILENT (\Answered \Seen) S: * 7 FETCH (MODSEQ (12121245160)) S: A330 OK Store completed Both changes are reported in session 2... C: C360 NOOP S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (12121245160)) S: C360 OK Noop completed ...and only changes to shared flags are reported in session 3. C: D390 NOOP S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (12121245160)) S: D390 OK Noop completed Server implementers should also see for additional quality of implementation issues related to the FETCH command.

The MODSEQ criterion for the SEARCH (or UID SEARCH) command allows a client to search for the metadata items that were modified since a specified moment. Syntax: MODSEQ [<entry-name> <entry-type-req>] <mod-sequence-valzer> Messages that have modification values that are equal to or greater than <mod-sequence-valzer>. This allows a client, for example, to find out which messages contain metadata items that have changed since the last time it updated its disconnected cache. The client may also specify <entry-name> (name of the metadata item) and <entry-type-req> (type of metadata item) before <mod-sequence-valzer>. <entry-type-req> can be one of "shared", "priv" (private), or "all". The last means that the server MUST use the biggest value among "priv" and "shared" mod-sequences for the metadata item. If the server doesn't store separate mod-sequences for different metadata items, it MUST ignore <entry-name> and <entry-type-req>. Otherwise, the server should use them to narrow down the search. For a flag <flagname>, the corresponding <entry-name> has the form "/flags/<flagname>". Note that the leading "\" character that denotes a system flag has to be escaped as per Section 4.3 of , as <entry-name> uses the syntax for quoted strings (see the examples below). If the client specifies a MODSEQ criterion in a SEARCH (or UID SEARCH) command and the server returns a non-empty SEARCH result, the server MUST also append (to the end of the untagged SEARCH response) the highest mod-sequence for all messages being returned. See also . Note that other IMAP extensions such as ESEARCH can override this requirement (see for more details.)

C: a SEARCH MODSEQ "/flags/\\draft" all 620162338 S: * SEARCH 2 5 6 7 11 12 18 19 20 23 (MODSEQ 917162500) S: a OK Search complete In the above example, the message numbers of any messages having a mod-sequence equal to or greater than 620162338 for the "\Draft" flag are returned in the search results.

C: t SEARCH OR NOT MODSEQ 720162338 LARGER 50000 S: * SEARCH S: t OK Search complete, nothing found

Data: zero or more numbers mod-sequence value (omitted if no match) This document extends the syntax of the untagged SEARCH response to include the highest mod-sequence for all messages being returned. If a client specifies a MODSEQ criterion in a SEARCH (or UID SEARCH) command and the server returns a non-empty SEARCH result, the server MUST also append (to the end of the untagged SEARCH response) the highest mod-sequence for all messages being returned. See for examples.

This document defines a new status data item: The highest mod-sequence value of all messages in the mailbox. This is the same value that is returned by the server in the HIGHESTMODSEQ response code in an OK untagged response (see ). If the server doesn't support the persistent storage of mod-sequences for the mailbox (see ), the server MUST return 0 as the value of the HIGHESTMODSEQ status data item.

C: A042 STATUS blurdybloop (UIDNEXT MESSAGES HIGHESTMODSEQ) S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292 HIGHESTMODSEQ 7011231777) S: A042 OK STATUS completed

The CONDSTORE extension defines a single optional select parameter, "CONDSTORE", which tells the server that it MUST include the MODSEQ FETCH response data items in all subsequent unsolicited FETCH responses. The CONDSTORE parameter to SELECT/EXAMINE helps avoid a race condition that might arise when one or more metadata items are modified in another session after the server has sent the HIGHESTMODSEQ response code and before the client was able to issue a CONDSTORE enabling command.

C: A142 SELECT INBOX (CONDSTORE) S: * 172 EXISTS S: * 1 RECENT S: * OK [UNSEEN 12] Message 12 is first unseen S: * OK [UIDVALIDITY 3857529045] UIDs valid S: * OK [UIDNEXT 4392] Predicted next UID S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited S: * OK [HIGHESTMODSEQ 715194045007] S: A142 OK [READ-WRITE] SELECT completed, CONDSTORE is now enabled

The MODSEQ Search Criterion (see ) causes modifications to SORT responses similar to modifications to SEARCH responses defined in :

SORT Response Data: zero or more numbers mod-sequence value (omitted if no match) This document extends the syntax of the untagged SORT response to include the highest mod-sequence for all messages being returned. If a client specifies a MODSEQ criterion in a SORT (or UID SORT) command and the server returns a non-empty SORT result, the server MUST also append (to the end of the untagged SORT response) the highest mod-sequence for all messages being returned. Note that other IMAP extensions such as ESORT can override this requirement (see for more details.) THREAD commands that include a MODSEQ Search Criterion return THREAD responses as specified in , i.e., THREAD responses are unchanged by the CONDSTORE extension.

If a client specifies a MODSEQ criterion in an extended SEARCH (or extended UID SEARCH) command and the server returns a non-empty SEARCH result, the server MUST return the ESEARCH response containing the MODSEQ result option as defined in Section 3.2 of .

C: a SEARCH RETURN (ALL) MODSEQ 1234 S: * ESEARCH (TAG "a") ALL 1:3,5 MODSEQ 1236 S: a OK Extended SEARCH completed If a client specifies a MODSEQ criterion in an extended SORT (or extended UID SORT) command and the server returns a non-empty SORT result, the server MUST return the ESEARCH response containing the MODSEQ result option defined in Section 3.2 of .

C: a SORT RETURN (ALL) (DATE) UTF-8 MODSEQ 1234 S: * ESEARCH (TAG "a") ALL 5,3,2,1 MODSEQ 1236 S: a OK Extended SORT completed

Server implementations should follow the following rule, which applies to any successfully completed STORE/UID STORE (with and without an UNCHANGEDSINCE modifier), as well as to a FETCH command that implicitly sets the \Seen flag: Adding the flag when it is already present or removing it when it is not present SHOULD NOT change the mod-sequence. This will prevent spurious client synchronization requests. However, note that client implementers MUST NOT rely on this server behavior. A client can't distinguish between the case when a server has violated the SHOULD mentioned above and when one or more clients set and unset (or unset and set) the flag in another session.

This section describes how a server implementation that doesn't store separate per-metadata mod-sequences for different metadata items can avoid sending the MODIFIED response to any of the following conditional STORE operations: +FLAGS -FLAGS +FLAGS.SILENT -FLAGS.SILENT Note that the optimization described in this section can't be performed in case of a conditional STORE FLAGS (without "+" or "-") operation. Let's use the following example. The client has issued:

C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) +FLAGS.SILENT ($Processed) When the server receives the command and parses it successfully, it iterates through the message set and tries to execute the conditional STORE command for each message. Each server internally works as a client, i.e., it has to cache the current state of all IMAP flags as it is known to the client. In order to report flag changes to the client, the server compares the cached values with the values in its database for IMAP flags. Imagine that another client has changed the state of a flag \Deleted on the message 101 and that the change updated the mod-sequence for the message. The server knows that the mod-sequence for the mailbox has changed; however, it also knows that: the client is not interested in the \Deleted flag, as it hasn't included it in the +FLAGS.SILENT operation and the state of the flag $Processed hasn't changed (the server can determine this by comparing the cached flag state with the state of the flag in the database). Therefore, the server doesn't have to report MODIFIED to the client. Instead, the server may set the $Processed flag, update the mod-sequence for the message 101 once again, and send an untagged FETCH response with a new mod-sequence and flags:

S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed \Deleted \Answered)) See also for additional quality-of-implementation issues.

All protocol changes and requirements specified for the CONDSTORE extension are also a part of the QRESYNC extension. The QRESYNC extension puts additional requirements on a server implementing the CONDSTORE extension. Each mailbox that supports persistent storage of mod-sequences, i.e., for which the server would send a HIGHESTMODSEQ untagged OK response code on a successful SELECT/EXAMINE, MUST increment the per-mailbox mod-sequence when one or more messages are expunged due to EXPUNGE, UID EXPUNGE, CLOSE, or MOVE ; the server MUST associate the incremented mod-sequence with the UIDs of the expunged messages. Additionally, if the server also supports the IMAP METADATA extension , it MUST increment the per-mailbox mod-sequence when SETMETADATA successfully changes an annotation on the corresponding mailbox. A server implementing QRESYNC MUST send untagged events to a client in a way that the client doesn't lose any changes in case of connectivity loss. In particular, this means that if the server sends MODSEQ FETCH data items while EXPUNGE (or VANISHED) replies with lower mod-sequences being delayed, the server MUST send the HIGHESTMODSEQ response code with a lower value than the EXPUNGE's mod-sequence. See the example in .

A client that supports CONDSTORE but not QRESYNC might resynchronize a mailbox and discover that its HIGHESTMODSEQ has increased from the value cached by the client. If the increase is only due to messages having been expunged since the client last synchronized, the client is likely to send a FETCH ... CHANGEDSINCE command that returns no data. Thus, a client that supports CONDSTORE but not QRESYNC might incur a penalty of an unneeded round trip when resynchronizing some mailboxes (those that have had messages expunged but no flag changes since the last synchronization). This extra round trip is only incurred by clients that support CONDSTORE but not QRESYNC and only when a mailbox has had messages expunged but no flag changes to non-expunged messages. Since CONDSTORE is a relatively new extension, it is strongly encouraged that clients that support it also support QRESYNC.

The quick resync IMAP extension is present if an IMAP4 server returns "QRESYNC" as one of the supported capabilities to the CAPABILITY command. For compatibility with clients that only support the CONDSTORE IMAP extension, servers SHOULD also advertise "CONDSTORE" in the CAPABILITY response.

Servers supporting QRESYNC MUST implement and advertise support for the ENABLE IMAP extension. Also, the presence of the "QRESYNC" capability implies support for the CONDSTORE IMAP extension even if the "CONDSTORE" capability isn't advertised. A server compliant with this specification is REQUIRED to support "ENABLE QRESYNC" and "ENABLE QRESYNC CONDSTORE" (which are "CONDSTORE enabling commands", see , and have identical results). Note that the order of parameters is not significant, but there is no requirement for a compliant server to support "ENABLE CONDSTORE" by itself. The "ENABLE QRESYNC"/"ENABLE QRESYNC CONDSTORE" command also tells the server that it MUST start sending VANISHED responses (see ) instead of EXPUNGE responses for all mailboxes for which the server doesn't return the NOMODSEQ response code. This change remains in effect until the connection is closed. A client making use of QRESYNC MUST issue "ENABLE QRESYNC" once it is authenticated. A server MUST respond with a tagged BAD response if the QRESYNC parameter to the SELECT/EXAMINE command or the VANISHED UID FETCH modifier is specified and the client hasn't issued "ENABLE QRESYNC", or the server has not positively responded (in the current connection) to that command with the untagged ENABLED response containing QRESYNC.

Once a CONDSTORE enabling command is issued by the client, the server MUST automatically include both UID and mod-sequence data in all subsequent untagged FETCH responses (until the connection is closed), whether they were caused by a regular STORE/UID STORE, a STORE/UID STORE with an UNCHANGEDSINCE modifier, a FETCH/UID FETCH that implicitly set the \Seen flag, or an external agent. Note that this rule doesn't affect untagged FETCH responses caused by a FETCH command that doesn't include UID and/or a MODSEQ FETCH data item (and doesn't implicitly set the \Seen flag) or UID FETCH without the MODSEQ FETCH data item.

The Quick Resynchronization parameter to SELECT/EXAMINE commands has four arguments: the last known UIDVALIDITY, the last known modification sequence, the optional set of known UIDs, and an optional parenthesized list of known sequence ranges and their corresponding UIDs. A server MUST respond with a tagged BAD response if the Quick Resynchronization parameter to the SELECT/EXAMINE command is specified and the client hasn't issued "ENABLE QRESYNC" in the current connection, or the server has not positively responded to that command with the untagged ENABLED response containing QRESYNC. Before opening the specified mailbox, the server verifies all arguments for syntactic validity. If any parameter is not syntactically valid, the server returns the tagged BAD response, and the mailbox remains unselected. Once the check is done, the server opens the mailbox as if no SELECT/EXAMINE parameters are specified (this is subject to the processing of other parameters as defined in other extensions). In particular, this means that the server MUST send all untagged responses as specified in Sections 6.3.1 and 6.3.2 of . After that, the server checks the UIDVALIDITY value provided by the client. If the provided UIDVALIDITY doesn't match the UIDVALIDITY for the mailbox being opened, then the server MUST ignore the remaining parameters and behave as if no dynamic message data changed. The client can discover this situation by comparing the UIDVALIDITY value returned by the server. This behavior allows the client not to synchronize the mailbox or decide on the best synchronization strategy. Attempting to resynchronize INBOX, but the provided UIDVALIDITY parameter doesn't match the current UIDVALIDITY value.

C: A02 SELECT INBOX (QRESYNC (67890007 20050715194045000 41,43:211,214:541)) S: * 464 EXISTS S: * 3 RECENT S: * OK [UIDVALIDITY 3857529045] UIDVALIDITY S: * OK [UIDNEXT 550] Predicted next UID S: * OK [HIGHESTMODSEQ 90060128194045007] Highest mailbox mod-sequence S: * OK [UNSEEN 12] Message 12 is first unseen S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen) S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft \Deleted \Seen \*)] Permanent flags S: A02 OK [READ-WRITE] Sorry, UIDVALIDITY mismatch Remaining parameters are described in the following subsections.

A server that doesn't support the persistent storage of mod-sequences for the mailbox MUST send an OK untagged response including the NOMODSEQ response code with every successful SELECT or EXAMINE command (see ). Such a server doesn't need to remember mod-sequences for expunged messages in the mailbox. It MUST ignore the remaining parameters and behave as if no dynamic message data changed. If the provided UIDVALIDITY matches that of the selected mailbox, the server then checks the last known modification sequence. The server sends the client any pending flag changes (using FETCH responses that MUST contain UIDs) and expunges those that have occurred in this mailbox since the provided modification sequence. If the list of known UIDs was also provided, the server should only report flag changes and expunges for the specified messages. If the client did not provide the list of UIDs, the server acts as if the client has specified "1:<maxuid>", where <maxuid> is the mailbox's UIDNEXT value minus 1. If the mailbox is empty and never had any messages in it, then lack of the list of UIDs is interpreted as an empty set of UIDs. Thus, the client can process just these pending events and need not perform a full resynchronization. Without the message sequence number matching information, the result of this step is semantically equivalent to the client issuing: tag1 UID FETCH known-uids (FLAGS) (CHANGEDSINCE mod-sequence-value VANISHED) In particular, this means that all requirements specified in apply.

C: A03 SELECT INBOX (QRESYNC (67890007 90060115194045000 41:211,214:541)) S: * OK [CLOSED] S: * 100 EXISTS S: * 11 RECENT S: * OK [UIDVALIDITY 67890007] UIDVALIDITY S: * OK [UIDNEXT 600] Predicted next UID S: * OK [HIGHESTMODSEQ 90060115205545359] Highest mailbox mod-sequence S: * OK [UNSEEN 7] There are some unseen messages in the mailbox S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen) S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft \Deleted \Seen \*)] Permanent flags S: * VANISHED (EARLIER) 41,43:116,118,120:211,214:540 S: * 49 FETCH (UID 117 FLAGS (\Seen \Answered) MODSEQ (90060115194045001)) S: * 50 FETCH (UID 119 FLAGS (\Draft $MDNSent) MODSEQ (90060115194045308)) S: * 51 FETCH (UID 541 FLAGS (\Seen $Forwarded) MODSEQ (90060115194045001)) S: A03 OK [READ-WRITE] mailbox selected In the above example, flag information for UID 42 is not returned, presumably because its flags haven't changed since the MODSEQ 90060115194045000.

A client MAY provide a parenthesized list of a message sequence set and the corresponding UID sets. Both MUST be provided in ascending order. The server uses this data to restrict the range for which it provides expunged message information. Conceptually, the client provides a small sample of sequence numbers for which it knows the corresponding UIDs. The server then compares each sequence number and UID pair the client provides with the current state of the mailbox. If a pair matches, then the client knows of any expunges up to, and including, the message; thus, it will not include that range in the VANISHED response, even if the mod-sequence-value provided by the client is too old for the server to have data of when those messages were expunged. Thus, if the Nth message number in the first set in the list is 4, and the Nth UID in the second set in the list is 8, and the mailbox's fourth message has UID 8, then no UIDs equal to or less than 8 are present in the VANISHED response. If the (N+1)th message number is 12, and the (N+1)th UID is 24, and the (N+1)th message in the mailbox has UID 25, then the lowest UID included in the VANISHED response would be 9. In the following two examples, the server is unable to remember expunges at all, and only UIDs with messages divisible by three are present in the mailbox. In the first example, the client does not use the fourth parameter; in the second, it provides it. This example is somewhat extreme, but it shows that judicious usage of the sequence match data can save a substantial amount of bandwidth. Example:

C: A04 SELECT INBOX (QRESYNC (67890007 90060115194045000 1:29997)) S: * 10003 EXISTS S: * 4 RECENT S: * OK [UIDVALIDITY 67890007] UIDVALIDITY S: * OK [UIDNEXT 30013] Predicted next UID S: * OK [HIGHESTMODSEQ 90060115205545359] Highest mailbox mod-sequence S: * OK [UNSEEN 7] There are some unseen messages in the mailbox S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen) S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft \Deleted \Seen \*)] Permanent flags S: * VANISHED (EARLIER) 1:2,4:5,7:8,10:11,13:14,[...], 29668:29669,29671:29996 S: * 1 FETCH (UID 3 FLAGS (\Seen \Answered $Important) MODSEQ (90060115194045001)) S: ... S: * 9889 FETCH (UID 29667 FLAGS (\Seen \Answered) MODSEQ (90060115194045027)) S: * 9890 FETCH (UID 29670 FLAGS (\Draft $MDNSent) MODSEQ (90060115194045028)) S: ... S: * 9999 FETCH (UID 29997 FLAGS (\Seen $Forwarded) MODSEQ (90060115194045031)) S: A04 OK [READ-WRITE] mailbox selected B04 SELECT INBOX (QRESYNC (67890007 90060115194045000 1:29997 (5000,7500,9000,9990:9999 15000, 22500,27000,29970,29973,29976,29979,29982,29985,29988,29991, 29994,29997))) * 10003 EXISTS * 4 RECENT * OK [UIDVALIDITY 67890007] UIDVALIDITY * OK [UIDNEXT 30013] Predicted next UID * OK [HIGHESTMODSEQ 90060115205545359] Highest mailbox mod-sequence * OK [UNSEEN 7] There are some unseen messages in the mailbox * FLAGS (\Answered \Flagged \Draft \Deleted \Seen) * OK [PERMANENTFLAGS (\Answered \Flagged \Draft \Deleted \Seen \*)] Permanent flags * 1 FETCH (UID 3 FLAGS (\Seen \Answered $Important) MODSEQ (90060115194045001)) ... * 9889 FETCH (UID 29667 FLAGS (\Seen \Answered) MODSEQ (90060115194045027)) * 9890 FETCH (UID 29670 FLAGS (\Draft $MDNSent) MODSEQ (90060115194045028)) ... * 9999 FETCH (UID 29997 FLAGS (\Seen $Forwarded) MODSEQ (90060115194045031)) B04 OK [READ-WRITE] mailbox selected

has extended the syntax of the FETCH and UID FETCH commands to include an optional FETCH modifier. This document defines a new UID FETCH modifier: VANISHED. Note that the VANISHED UID FETCH modifier is NOT allowed with a FETCH command. The server MUST return a tagged BAD response if this response is specified as a modifier to the FETCH command. A server MUST respond with a tagged BAD response if the VANISHED UID FETCH modifier is specified and the client hasn't issued "ENABLE QRESYNC" in the current connection. The VANISHED UID FETCH modifier MUST only be specified together with the CHANGEDSINCE UID FETCH modifier. If the VANISHED UID FETCH modifier is used without the CHANGEDSINCE UID FETCH modifier, the server MUST respond with a tagged BAD response. The VANISHED UID FETCH modifier instructs the server to report those messages from the UID set parameter that have been expunged and whose associated mod-sequence is larger than the specified mod-sequence. That is, the client requests to be informed of messages from the specified set that were expunged since the specified mod-sequence. Note that the mod-sequence(s) associated with these messages was updated when the messages were expunged (as described above). The expunged messages are reported using the VANISHED (EARLIER) response as described in . Any VANISHED (EARLIER) responses MUST be returned before any FETCH responses, otherwise the client might get confused about how message numbers map to UIDs. Note: A server that receives a mod-sequence smaller than <minmodseq>, where <minmodseq> is the value of the smallest expunged mod-sequence it remembers minus one, MUST behave as if it was requested to report all expunged messages from the provided UID set parameter.

Example 1: Without the VANISHED UID FETCH modifier, a CONDSTORE-aware client needs to issue separate commands to learn of flag changes and expunged messages since the last synchronization: C: s100 UID FETCH 300:500 (FLAGS) (CHANGEDSINCE 12345) S: * 1 FETCH (UID 404 MODSEQ (65402) FLAGS (\Seen)) S: * 2 FETCH (UID 406 MODSEQ (75403) FLAGS (\Deleted)) S: * 4 FETCH (UID 408 MODSEQ (29738) FLAGS ($NoJunk $AutoJunk $MDNSent)) S: s100 OK FETCH completed C: s101 UID SEARCH 300:500 S: * SEARCH 404 406 407 408 410 412 S: s101 OK search completed Where 300 and 500 are the lowest and highest UIDs from the client's cache. The second SEARCH response tells the client that the messages with UIDs 407, 410, and 412 are still present, but their flags haven't changed since the specified modification sequence.

Using the VANISHED UID FETCH modifier, it is sufficient to issue only a single command: C: s100 UID FETCH 300:500 (FLAGS) (CHANGEDSINCE 12345 VANISHED) S: * VANISHED (EARLIER) 300:310,405,411 S: * 1 FETCH (UID 404 MODSEQ (65402) FLAGS (\Seen)) S: * 2 FETCH (UID 406 MODSEQ (75403) FLAGS (\Deleted)) S: * 4 FETCH (UID 408 MODSEQ (29738) FLAGS ($NoJunk $AutoJunk $MDNSent)) S: s100 OK FETCH completed

none untagged responses: EXPUNGE or VANISHED OK - expunge completed NO - expunge failure: can't expunge (e.g., permission denied) BAD - command unknown or arguments invalid This section updates the definition of the EXPUNGE command described in Section 6.4.3 of . The EXPUNGE command permanently removes all messages that have the \Deleted flag set from the currently selected mailbox. Before returning an OK to the client, those messages that are removed are reported using a VANISHED response or EXPUNGE responses. If the server is capable of storing modification sequences for the selected mailbox, it MUST increment the per-mailbox mod-sequence if at least one message was permanently removed due to the execution of the EXPUNGE command. For each permanently removed message, the server MUST remember the incremented mod-sequence and corresponding UID. If at least one message got expunged and QRESYNC was enabled, the server MUST send the updated per-mailbox modification sequence using the HIGHESTMODSEQ response code (see ) in the tagged OK response.

Example: C: A202 EXPUNGE S: * 3 EXPUNGE S: * 3 EXPUNGE S: * 5 EXPUNGE S: * 8 EXPUNGE S: A202 OK [HIGHESTMODSEQ 20010715194045319] expunged Note: In this example, the client hasn't enabled QRESYNC, so the server is still using untagged EXPUNGE responses. Note that the presence of the HIGHESTMODSEQ response code is optional in this case. If the selected mailbox returned NOMODSEQ, the HIGHESTMODSEQ response code will be absent. In this example, messages 3, 4, 7, and 11 had the \Deleted flag set. The first "* 3 EXPUNGE" reports message #3 as expunged. The second "* 3 EXPUNGE" reports message #4 as expunged (the message number was decremented due to the previous EXPUNGE response). See the description of the EXPUNGE response in for further explanation.

Once the client enables QRESYNC, the server will always send VANISHED responses instead of EXPUNGE responses for mailboxes that support the storing of modification sequences, so the previous example might look like this: Example: C: B202 EXPUNGE S: * VANISHED 405,407,410,425 S: B202 OK [HIGHESTMODSEQ 20010715194045319] expunged Here, messages with message numbers 3, 4, 7, and 11 have respective UIDs 405, 407, 410, and 425.

none no specific responses for this command OK - close completed, now in authenticated state BAD - command unknown or arguments invalid This section updates the definition of the CLOSE command described in Section 6.4.2 of . The CLOSE command permanently removes all messages that have the \Deleted flag set from the currently selected mailbox and returns to the authenticated state from the selected state. No untagged EXPUNGE (or VANISHED) responses are sent. If the server is capable of storing modification sequences for the selected mailbox, it MUST increment the per-mailbox mod-sequence if at least one message was permanently removed due to the execution of the CLOSE command. For each permanently removed message, the server MUST remember the incremented mod-sequence and corresponding UID. The server MUST NOT send the updated per-mailbox modification sequence using the HIGHESTMODSEQ response code (see ) in the tagged OK response, as this might cause loss of synchronization on the client.

Example: C: A202 CLOSE S: A202 OK done

message set untagged responses: EXPUNGE or VANISHED OK - expunge completed NO - expunge failure: can't expunge (e.g., permission denied) BAD - command unknown or arguments invalid This section updates the definition of the UID EXPUNGE command described in Section 2.1 of , in the presence of QRESYNC. Servers that implement both and QRESYNC extensions must implement UID EXPUNGE as described in this section. The UID EXPUNGE command permanently removes from the currently selected mailbox all messages that have both the \Deleted flag set and a UID that is included in the specified message set. If a message either does not have the \Deleted flag set or has a UID that is not included in the specified message set, it is not affected. This command is particularly useful for disconnected mode clients. By using UID EXPUNGE instead of EXPUNGE when resynchronizing with the server, the client can avoid inadvertently removing any messages that have been marked as \Deleted by other clients between the time that the client was last connected and the time the client resynchronizes. Before returning an OK to the client, those messages that are removed are reported using a VANISHED response or EXPUNGE responses. If the server is capable of storing modification sequences for the selected mailbox, it MUST increment the per-mailbox mod-sequence if at least one message was permanently removed due to the execution of the UID EXPUNGE command. For each permanently removed message, the server MUST remember the incremented mod-sequence and corresponding UID. If at least one message got expunged and QRESYNC was enabled, the server MUST send the updated per-mailbox modification sequence using the HIGHESTMODSEQ response code (see ) in the tagged OK response.

Example: C: . UID EXPUNGE 3000:3002 S: * 3 EXPUNGE S: * 3 EXPUNGE S: * 3 EXPUNGE S: . OK [HIGHESTMODSEQ 20010715194045319] Ok Note: In this example, the client hasn't enabled QRESYNC, so the server is still using untagged EXPUNGE responses instead of VANISHED responses. Note that the presence of the HIGHESTMODSEQ response code is optional. If the selected mailbox returned NOMODSEQ, the HIGHESTMODSEQ response code will be absent. In this example, at least messages with message numbers 3, 4, and 5 (UIDs 3000 to 3002) had the \Deleted flag set. The first "* 3 EXPUNGE" reports message #3 as expunged. The second "* 3 EXPUNGE" reports message #4 as expunged (the message number was decremented due to the previous EXPUNGE response). See the description of the EXPUNGE response in for further explanation.

The VANISHED response reports that the specified UIDs have been permanently removed from the mailbox. This response is similar to the EXPUNGE response ; however, it can return information about multiple messages, and it returns UIDs instead of message numbers. The first benefit saves bandwidth, while the second is more convenient for clients that only use UIDs to access the IMAP server. The VANISHED response has the same restrictions on when it can be sent as does the EXPUNGE response (see below). Once a client has issued "ENABLE QRESYNC" (and the server has positively responded to that command with the untagged ENABLED response containing QRESYNC), the server MUST use the VANISHED response without the EARLIER tag instead of the EXPUNGE response for all mailboxes that don't return NOMODSEQ when selected. The server continues using VANISHED in lieu of EXPUNGE for the duration of the connection. In particular, this affects the EXPUNGE and UID EXPUNGE commands, as well as messages expunged in other connections. Such a VANISHED response MUST NOT contain the EARLIER tag. The VANISHED response has two forms. The first form contains the EARLIER tag, which signifies that the response was caused by a UID FETCH (VANISHED) or a SELECT/EXAMINE (QRESYNC) command. The second form doesn't contain the EARLIER tag and is used for announcing message removals within an already selected mailbox. Because clients handle the two different forms of the VANISHED response differently, servers MUST NOT combine them. Messages are reported in VANISHED responses with or without the EARLIER tag, as appropriate to the cause, and, if necessary, two VANISHED responses are sent (one with EARLIER and one without).

an EARLIER tag list of UIDs The VANISHED (EARLIER) response is caused by a UID FETCH (VANISHED) or a SELECT/EXAMINE (QRESYNC) command. This response is sent if the UID set parameter to the UID FETCH (VANISHED) command includes UIDs of messages that are no longer in the mailbox. When the client sees a VANISHED EARLIER response, it MUST NOT decrement message sequence numbers for each successive message in the mailbox.

list of UIDs Once a client has issued "ENABLE QRESYNC" (and the server has positively responded to that command with the untagged ENABLED response containing QRESYNC), the server MUST use the VANISHED response without the EARLIER tag instead of the EXPUNGE response for all mailboxes that don't return NOMODSEQ when selected. The server continues using VANISHED in lieu of EXPUNGE for the duration of the connection. In particular, this affects the EXPUNGE and UID EXPUNGE commands, as well as messages expunged in other connections. Such a VANISHED response MUST NOT contain the EARLIER tag. Unlike VANISHED (EARLIER), this response also decrements the number of messages in the mailbox and adjusts the message sequence numbers for the messages remaining in the mailbox to account for the expunged messages. Because of this housekeeping, it is not necessary for the server to send an EXISTS response to report the new message count. See the example at the end of this section. A VANISHED response without the EARLIER tag MUST refer only to messages that are visible to the client in the current session at the time the VANISHED response is sent. That is, servers MUST NOT send UIDs for previously expunged messages or messages that were not announced to the client via EXISTS. This means that each UID listed in a VANISHED response results in the client decrementing the message count by one. This is required to prevent a possible race condition where new arrivals for which the UID is not yet known by the client are immediately expunged. A VANISHED response MUST NOT be sent when no command is in progress, nor while responding to a FETCH, STORE, or SEARCH command. This rule is necessary to prevent a loss of synchronization of message sequence numbers between the client and server. A command is not "in progress" until the complete command has been received; in particular, a command is not "in progress" during the negotiation of command continuation. Note: UID FETCH, UID STORE, and UID SEARCH are different commands from FETCH, STORE, and SEARCH. A VANISHED response MAY be sent during a UID command. However, the VANISHED response MUST NOT be sent during a UID SEARCH command that contains message numbers in the search criteria. The update from the VANISHED response MUST be recorded by the client.

Example: Let's assume that there is the following mapping between message numbers and UIDs in the currently selected mailbox (here "D" marks messages with the \Deleted flag set, and "x" represents UIDs, which are not relevant for the example): Message numbers: 1 2 3 4 5 6 7 8 9 10 11 UIDs: x 504 505 507 508 x 510 x x x 625 \Deleted messages: D D D D

In the presence of the extension defined in this document: C: A202 EXPUNGE S: * VANISHED 505,507,510,625 S: A202 OK EXPUNGE completed

Without the QRESYNC extension, the same example might look like: C: A202 EXPUNGE S: * 3 EXPUNGE S: * 3 EXPUNGE S: * 5 EXPUNGE S: * 8 EXPUNGE S: A202 OK EXPUNGE completed

(Continuing from the previous example.) If subsequently messages with UIDs 504 and 508 got marked as \Deleted: C: A210 EXPUNGE S: * VANISHED 504,508 S: A210 OK EXPUNGE completed For Example, the last VANISHED response only contains UIDs of messages expunged since the previous VANISHED response.

To illustrate the difference between VANISHED and VANISHED (EARLIER), suppose the mailbox contains UIDs 2 and 4. Any of the following responses would constitute a broken server implementation: S: * VANISHED 1 S: * VANISHED 3 S: * VANISHED 5 However, any of these UIDs can easily be referenced by the VANISHED (EARLIER) response.

The CLOSED response code has no parameters. A server implementing the extension defined in this document MUST return the CLOSED response code when the currently selected mailbox is closed implicitly using the SELECT/EXAMINE command on another mailbox. The CLOSED response code serves as a boundary between responses for the previously opened mailbox (which was closed) and the newly selected mailbox; all responses before the CLOSED response code relate to the mailbox that was closed, and all subsequent responses relate to the newly opened mailbox. A server that advertises "QRESYNC" or "CONDSTORE" in the capability string must return the CLOSED response code in this case, whether or not a CONDSTORE enabling command was issued. There is no need to return the CLOSED response code on completion of the CLOSE or the UNSELECT command (or similar), whose purpose is to close the currently selected mailbox without opening a new one.