This documentation is for Dovecot v2.x, see wiki1 for v1.x documentation.

imapc storage

The imapc storage accesses a remote IMAP server as if it were a regular Dovecot mailbox format. Dovecot can treat it as a very dummy storage or optionally a more capable storage.

# In-memory index files:
mail_location = imapc:

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

Connection settings

Do a regular IMAP LOGIN to using a LOGIN secret:

imapc_host =
imapc_password = secret
imapc_port = 143
imapc_user =

If you want to use a master user login, set:

imapc_master_user = masteruser

For SSL, use either:

For testing you may want to disable all SSL certificate checks:

imapc_ssl_verify = no

You can use other SASL mechanisms besides PLAIN by specifying (the first one advertised by IMAP server is used):

imapc_sasl_mechanisms = external plain login

The SASL client mechanisms are implemented in Dovecot's lib-sasl/ code. It's possible to add more with plugins.

Other settings

How long to wait for an IMAP command to reply before disconnecting and retrying (default: 5 mins).

Access only mailboxes under this prefix. For example imapc_list_prefix=INBOX/

Send something (NOOP/DONE) to server after not sending anything for this amount of time (default: 29 mins).
Log all IMAP traffic input/output to this directory.

Features and workarounds

imapc_features setting is a space-separated list of features and workarounds that can be enabled.



Allow passing through message sizes using FETCH RFC822.SIZE


Allow fetching specific message headers using FETCH BODY.PEEK[HEADER.FIELDS (..)]

Allow fetching BODY and BODYSTRUCTURE from remote server. (v2.2.30+)

Allow using SEARCH command.


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 (to be used for migrating only archived emails in "All Mails"). Add pop3_deleted_flag to mails that don't exist in POP3 server.
Use Sun/Oracle IMAP-server specific PROXYAUTH command to do master user authentication. Normally this would be done using the SASL PLAIN authentication.
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.
Access MODSEQ and HIGHESTMODSEQ (v2.2.24+)
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+)


Using the "imapc" quota backend allows asking for the quota from remote IMAP server (v2.2.30+). By default it uses GETQUOTAROOT INBOX for getting the quota. There are also two parameters that can be used to control how the quota is looked up:

For example:

plugin {
  quota = imapc:root=User Quota



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.

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.
Try to ignore wrong message sequence numbers in FETCH replies whenever possible, preferring to use the returned UID number instead.

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.

None: MailboxFormat/imapc (last edited 2019-02-13 12:35:03 by AkiTuomi)