Imapc Configuration

See Imapc for a technical description of Dovecot’s imapc mailbox format.

Mail Location Configuration Examples

# In-memory index files:
mail_location = imapc:

# Store index files locally:
mail_location = imapc:~/imapc

Connection Settings


  • Default: 5 mins

  • Values: Time

How long to wait for a reply to an IMAP command sent to the remote IMAP server before disconnecting and retrying.


How many times to retry connection against a remote IMAP server?


How long to wait between retries against a remote IMAP server?


  • Default: <empty>

  • Values: String

A space-separated list of features, optimizations, and workarounds that can be enabled.


  • delay-login: Don’t connect to the remote server until some command requires it. By default the server is connected to immediately on login. (v2.2.29+)

  • gmail-migration: Enable GMail-specific migration. Use IMAP X-GM-MSGID as POP3 UIDL. Add $GMailHaveLabels keyword to mails that have X-GM-LABELS except for \Muted keyword (to be used for migrating only archived emails in All Mails). Add pop3_deleted_flag to mails that don’t exist in POP3 server.

  • modseq: Access MODSEQ and HIGHESTMODSEQ (v2.2.24+).

  • proxyauth: Use Sun/Oracle IMAP-server specific PROXYAUTH command to do master user authentication. Normally this would be done using the SASL PLAIN authentication.

  • throttle:<INIT>:<MAX>:<SHRINK>: When receiving [THROTTLED] response (from GMail), throttling is applied. INIT = initial throttling msecs (default: 50 ms), afterwards each subsequent [THROTTLED] doubles the throttling until MAX is reached (default: 16000 ms). When [THROTTLED] is not received for a while, it’s shrank again. The initial shrinking is done after SHRINK (default: 500 ms). If [THROTTLED] is received again within this timeout, it’s doubled, otherwise both throttling and the next shrinking timeout is shrank to 3/4 the previous value.

New in version 2.3.15.

  • acl: When this feature is enabled and the imap-acl plugin is loaded, using a remote location via imapc will make IMAP ACL commands (MYRIGHTS, GETACL, SETACL, DELETEACL) proxied to the remote.


  • fetch-bodystructure: Allow fetching BODY and BODYSTRUCTURE FETCH BODY.PEEK[HEADER.FIELDS (..)].

  • fetch-headers: Allow fetching specific message headers using from remote server. (v2.2.30+)

  • rfc822.size: Allow passing through message sizes using FETCH RFC822.SIZE.

  • search: Allow using SEARCH command.


  • fetch-fix-broken-mails: If a FETCH returns NO (but not NO [LIMIT] or NO [SERVERBUG]), assume the mail is broken in server and just treat it as if it were an empty email. NOTE: This is often a dangerous option! It’s not safe to assume that NO means a permanent error rather than a temporary error. This feature should be enabled only for specific users who have been determined to be broken.

  • fetch-msn-workarounds: Try to ignore wrong message sequence numbers in FETCH replies whenever possible, preferring to use the returned UID number instead.

  • no-examine: Use SELECT instead of EXAMINE even when we don’t want to modify anything in the mailbox. This is a Courier-workaround where it didn’t permanently assign UIDVALIDITY to an EXAMINEd mailbox, but assigned it for SELECTed mailbox.

  • zimbra-workarounds: Fetch full message using BODY.PEEK[HEADER] BODY.PEEK[TEXT] instead of just BODY.PEEK[] because the header differs between these two when there are illegal control chars or 8bit chars. This mainly caused problems with dsync, but as of v2.2.22+ this should no longer be a problem and there’s probably no need to enable this workaround.


  • Default: <empty>

  • Values: String

The remote IMAP host to connect to.


  • Default: <empty>

  • Values: String

Access only mailboxes under this prefix.

Example, for a source IMAP server that uses an INBOX namespace prefix:

imapc_list_prefix = INBOX/


  • Default: <empty>

  • Values: String

The master username to authenticate as on the remote IMAP host.

To authenticate as a master user but use a separate login user, the following configuration should be employed, where the credentials are represented by masteruser and masteruser-secret:

imapc_user = %u
imapc_master_user = masteruser
imapc_password = masteruser-secret

Mail user variables can be used.

See also imapc_password. See also imapc_user.


  • Default: 29 mins

  • Values: Time

Send a command to the source IMAP server as a keepalive after no other command has been sent for this amount of time.

Dovecot will send either NOOP or DONE to the source IMAP server.


  • Default: 0

  • Values: Size

The maximum line length to accept from the remote IMAP server.

This setting is used to limit maximum memory usage.

A value of 0 indicates no maximum.


  • Default: <empty>

  • Values: String

The authentication password for the remote IMAP server.

If using master users, this setting will be the password of the master user.

See also imapc_master_user. See also imapc_user.


The port on the remote IMAP host to connect to.


  • Default: <empty>

  • Values: String

Log all IMAP traffic input/output to this directory.



  • Default: <empty>

  • Values: String

The SASL mechanisms to use for authentication when connection to a remote IMAP server.

The first one advertised by the remote IMAP sever is used.

PLAIN authentication will be used by default.

imapc_sasl_mechanisms = external plain login


  • Default: <empty>

  • Values: <empty>, no, imaps, starttls

Use TLS to connect to the remote IMAP server.

Settings: * <empty> or no: No TLS * imaps: Explicitly connect to remote IMAP port using TLS * starttls: Use IMAP STARTTLS command to switch to TLS connection


Verify remote IMAP TLS certificate?

Verification may be disabled during testing, but should be enabled during production use.

Only used if imapc_ssl is enabled.


  • Default: <empty>

  • Values: String

The user identity to be used for performing a regular IMAP LOGIN to the source IMAP server in dsync-based migration of mail.

Mail user variables can be used.

See also imapc_master_user. See also imapc_password.

Usage Examples

Do a regular IMAP LOGIN, using STARTTLS, to

imapc_host =
imapc_password = secret
imapc_port = 143
imapc_ssl = starttls
imapc_user =


Using the imapc quota backend allows asking for the quota from remote IMAP server (v2.2.30+). By default it uses GETQUOTAROOT INBOX to retrieve the quota.

There are two parameters that can be used to control how the quota is looked up:

  • box = <mailbox>: Use GETQUOTAROOT <mailbox>

  • root = <name>: Use GETQUOTA <name>


plugin {
  quota = imapc:root=User Quota