Provided by: dovecot-core_2.4.1+dfsg1-5ubuntu1_amd64 
NAME
doveadm-sync - Dovecot's two-way mailbox synchronization feature
SYNOPSIS
doveadm [GLOBAL OPTIONS] sync [-u user | -A | -F file | --no-userdb-lookup] [-S socket_path] [-1fPR] [-l
secs] [-r rawlog path] [-m mailbox] [-g mailbox guid] [-n namespace | -N] [-x exclude] [-a all mailbox]
[-s state] [-T secs] [-t start date] [-e end date] [-O sync flag] [-I max size] [-p setting=value]
destination
doveadm [GLOBAL OPTIONS] backup [-u user | -A | -F file | --no-userdb-lookup] [-S socket_path] [-fPR] [-l
secs] [-r rawlog path] [-m mailbox] [-g mailbox guid] [-n namespace | -N] [-x exclude] [-a all mailbox]
[-s state] [-T secs] [-t start date] [-e end date] [-O sync flag] [-I max size] [-p setting=value]
destination
DESCRIPTION
dsync (short for doveadm sync) is Dovecot's mailbox synchronization feature. It can be used for several
different use cases: Two-way synchronization of mailboxes, creating backups of mails, and convert
mailboxes from/to different mailbox formats. All of these can be used within the same server or between
different servers (via ssh(1) or tcp connections). Remote mailboxes can be accessed also via IMAP
protocol, which allows using dsync for mailbox migration purposes.
You can run dsync in one of three modes:
• doveadm backup performs one-way synchronization. If there are any changes in the destination they
will be reverted, so the destination will look exactly like the source.
• doveadm sync performs two-way synchronization. It merges all changes without losing anything. Both
the mailboxes will end up looking identical after the synchronization is finished.
• doveadm sync -1 performs one-way synchronization. If there are any changes in the destination, they
will be preserved and the new changes will be merged on top of them. This merging doesn't currently
work perfectly, so its use should be limited. Its main purpose is that during mailbox migration you
can run doveadm backup multiple times, then switch mails to be delivered to the new mailbox and run
doveadm sync -1 once more to transfer any last new mails from the old mailbox.
• The one-way algorithm is the same as two-way dsync algorithm except the source account is not
modified. It fetches the message's GUID (Global UID), which is used to identify any conflicting
UIDs in messages. As long as the source and destination side has matching UID<->GUID mapping,
those emails are assumed to be synced correctly. Only after the first mismatch will changes
begin.
Example: Source mailbox has messages UID 1..5; source mailbox is sync'd using doveadm backup to the
destination. Subsequently, UID 6 is delivered to the source mailbox and UID 1 is expunged from the
destination mailbox. In this example, UID 1 is kept removed (in destination) because UID 1..5 have
identical Date+Message-ID headers. UID 6 is not seen in destination so it's copied.
If both source and destination have UID 6, but the messages are different, the headers don't match
and both the messages are kept in the destination but they're given new UIDs 7 and 8 just to be sure
any client didn't get confused about what UID 6 actually was. Thus, one-way sync begins to quickly
diverge from the source mailbox once changes start to occur on either side; one-way sync should
therefore normally only be used within a short period of time after a doveadm backup or doveadm sync
command was used to synchronize the mailboxes.
There are also three different synchronization algorithms:
• Full synchronization (-f parameter) scans through all the messages in all the mailboxes. This
guarantees that everything will be synchronized, but it's unnecessarily slow for incremental
synchronization.
• Fast synchronization (default) first attempts to find mailboxes that have changed, and synchronize
only those. This is done by checking the mailboxes' metadata (NEXTUID and HIGHESTMODSEQ). Usually
this works fine, especially with one-way synchronization, but if both sides do exactly the same
number of changes, the metadata may end up containing the same values even if the changes were
different.
• Stateful synchronization (-s parameter) is the most efficient way to synchronize mailboxes. It relies
on having the earlier dsync run's state saved somewhere and being passed to the next dsync run. Based
on this state dsync can send only the changes that happened after the previous dsync run. As long as
the state or the mailboxes aren't corrupted this algorithm should work perfectly.
The syncing is done as perfectly as possible: an IMAP or a POP3 client shouldn't be able to notice any
differences between the two mailboxes. Two-way syncing means that it's safe to do any kind of
modifications in both sides, and dsync will merge the changes without losing any changes done on either
side. This is possible because dsync can access Dovecot's index logs that keep track of changes. It's of
course possible to have conflicts during merging, these are resolved in a safe way. See the dsync design
document for more information.
dsync uses the same configuration files as the rest of Dovecot (via doveconf(1)). The entire
configuration can be changed by giving -c parameter to another configuration file, or using -o parameter
to override specific settings. When executing a remote dsync program it works the same way: it uses its
own local configuration.
dsync can be run completely standalone. It doesn't require any Dovecot server processes to be running,
except when using -u parameter to do a userdb lookup from auth process.
dsync can sync either one or multiple users using the -u or -A parameters.
GLOBAL OPTIONS
Global doveadm(1)
-D
Enables verbosity and debug messages.
-O
Do not read any config file, just use defaults. The dovecot_storage_version setting defaults to the
latest version, but can be overridden with
-k
Preserve entire environment for doveadm, not just import_environment setting.
-v
Enables verbosity, including progress counter.
-i instance-name
If using multiple Dovecot instances, choose the config file based on this instance name.
See instance_name setting for more information.
-c config-file
Read configuration from the given config-file. By default it first reads config socket, and then
falls back to /etc/dovecot/dovecot.conf. You can also point this to config socket of some instance
running compatible version.
-o setting=value
Overrides the configuration setting from /etc/dovecot/dovecot.conf and from the userdb with the given
value. In order to override multiple settings, the -o option may be specified multiple times.
OPTIONS
-A
If the -A option is present, the command will be performed for all users. Using this option in
combination with system users from userdb { driver = passwd } is not recommended, because it contains
also users with a lower UID than the one configured with the first_valid_uid setting.
When the SQL userdb module is used, make sure that the userdb_sql_iterate_query setting setting
matches your database layout.
When using the LDAP userdb module, make sure that the userdb_fields setting and
userdb_ldap_iterate_fields setting settings match your LDAP schema. Otherwise doveadm(1) will be
unable to iterate over all users.
-F file
Execute the command for all the users in the file. This is similar to the -A option, but instead of
getting the list of users from the userdb, they are read from the given file. The file contains one
username per line.
-1
Do one-way synchronization instead of two-way synchronization.
-f
Do full synchronization.
-N
Synchronize all the available namespaces. By default only the inbox=yes namespace is synchronized.
--no-userdb-lookup
Do not perform userdb lookup. Use the USER environment variable to specify the username.
-P
Run a doveadm-purge(1) for the destination (remote) storage after synchronization.
-R
Do a reverse sync. Normally, messages would be pushed from the local system to the destination
(remote). This option reverses the flow, and will instead pull messages from the remote to the local
storage.
-S socket_path
The option's argument is either an absolute path to a local UNIX domain socket, or a hostname and
port (hostname:port), in order to connect a remote host via a TCP socket.
This allows an administrator to execute doveadm(1) mail commands through the given socket.
-T secs
Specify the time in seconds, how long doveadm(1) should wait for stalled I/O operations. The default
timeout is 600 seconds.
-p setting=value
Overrides the configuration setting for source storage.
-p setting=value
Overrides the configuration setting for source storage.
-g mailbox_guid
Same as -m, but find the mailbox to be synchronized by its GUID instead of by name.
-l secs
Lock the dsync for this user. Wait for maximum secs before giving up. This parameter should be used
to avoid broken synchronization if it's possible that dsync is being run concurrently for the same
user.
-m mailbox
Synchronize only this mailbox name.
-n namespace
Synchronize only the specified namespace. This parameter can be used multiple times.
-a all mailbox
Name for the "All mails" virtual mailbox. If specified, mails are attempted to be copied from this
mailbox instead of being saved separately. This may reduce the total disk space usage as well as disk
IO.
-t start date
Skip any mails whose received-timestamp is older than the specified time.
-e end date
Skip any mails whose received-timestamp is newer than the specified time.
-O sync flag
Sync only mails that have the specified flag. If the flag name begins with "-", sync all mails except
the ones with the specified flag.
-I max size
Skip any mails larger than the specified size.
-r rawlog_path
Running dsync remotely, write the remote input/output traffic to the specified log file.
-s previous_state
Use stateful synchronization. If the previous state is unknown, use an empty string. The new state is
always printed to standard output.
-u user/mask
Run the command only for the given user. It's also possible to use '*' and '?' wildcards (e.g. -u
*@example.org).
-x mailbox_mask
Exclude the specified mailbox name/mask. The mask may contain "?" and "*****" wildcards. The mask can
also be a special-use name (e.g. \Trash). This parameter can be used multiple times.
ARGUMENTS
destination
This argument specifies the synchronized destination.
It can be one of:
mail_driver:mail_path : Uses the storage specified by mail_driver and mail_path. Use the -p
parameter to specify additional settings.
remote: login@host : Uses dsync_remote_cmd setting to connect to the remote host (usually via ssh)
remoteprefix:login@host : This is the same as remote, except "user@domain\n" is sent before dsync
protocol starts. This allows implementing a trusted wrapper script that runs doveadm dsync-server by
reading the username from the first line.
tcp: host[:port] : Connects to remote doveadm server via TCP. The default port is specified by
doveadm_port setting.
tcps: host[:port] : This is the same as tcp, but with SSL.
command [arg1 [, arg2, ...]] : Runs a local command that connects its standard input & output to a
dsync server.
EXIT STATUS
dsync will exit with one of the following values:
0
Synchronization was done perfectly.
2
Synchronization was done without errors, but some changes couldn't be done, so the mailboxes aren't
perfectly synchronized. Running dsync again usually fixes this. Typically this occurs for message
modification sequences with newly created mailboxes. It can also occur if one of the mailboxes change
during the syncing.
1, >2
Synchronization failed.
See also doveadm(1) for other possible error codes.
EXAMPLE
SYNCHRONIZATION
Synchronize mailboxes with a remote server. Any errors are written to stderr:
doveadm sync -u username@example.com remote:server-replica.example.com
If you need more complex parameters to ssh, you can use e.g.:
doveadm sync -u username@example.com ssh -i id_dsa.dovecot \
mailuser@example.com doveadm dsync-server -u username@example.com
CONVERTING
Example to convert mails from Maildir format to the format specified in the configuration file:
doveadm backup -u user maildir:~/Maildir
If you want to do this without any downtime, you can do the conversion one user at a time. Initially:
• Configuration uses mail_driver = maildir and mail_path = ~/Maildir
• Set up the possibility of doing per-user mail location using userdb extra fields.
Then for each user:
1. Run doveadm sync once to do the initial conversion.
2. Run doveadm sync again, because the initial conversion could have taken a while and new changes could
have occurred during it. This second time only applies changes, so it should be fast.
3. Update userdb to return the wanted new mail format configuration. For example: mail_driver = mdbox
and mail_path = ~/mdbox. If you're using auth cache, you need to flush it, e.g. doveadm auth cache
flush.
4. Wait for a few seconds and then kill (doveadm kick) the user's all existing imap and pop3 sessions
(that are still using maildir).
5. Run doveadm sync once more to apply final changes that were possibly done. After this there should be
no changes to Maildir, because the user's mail location has been changed and all existing processes
using it have been killed.
Once all users have been converted, you can update the global mail_driver and mail_path settings and
remove the per-user mail locations from userdb.
REPORTING BUGS
Report bugs, including doveconf -n output, to the Dovecot Mailing List ⟨dovecot@dovecot.org⟩. Information
about reporting bugs is available at: https://dovecot.org/bugreport.html
SEE ALSO
doveadm(1), doveadm-purge(1)
78ffb79 March 2025 DOVEADM-SYNC(1)