Hi,

I'm experiencing serious issues when using doveadm sync not working at all or do not properly sync. I wanted to use this for migrating external mailboxes to my server (in order to overcome the time when some servers/clients still use the old server and some already the my server).

I tried to find a few steps in order to replicate this: For testing purposes I simulate both the remote and local server on my Dovecot instance. I created remote@DOMAIN.TLD and local@DOMAIN.TLD both use mdbox and are empty (i.e., the mail_location is still non-existent).

Then I send two mails to remote@DOMAIL.TLD (Subjects: Test1 and Test2).

Start backup remote IMAP account (remote@DOMAIN.TLD) to local account (local@DOMAIN.TLD):

• doveadm -o imapc_user="remote@DOMAIN.TLD" -o imapc_password="PW" -o imapc_host="localhost" -o mail_prefetch_count=20 -o imapc_features="rfc822.size fetch-headers" backup -R -u local@DOMAIN.TLD imapc: (without this I often got errors such as "Error: Backend didn't update mailbox Trash GUID" on sync runs, which seems to be an unrecoverable error).

Now the two mailboxes seem to be the same (can confirm this when logging into the two mailboxes).

Now, run first sync:

• doveadm -o imapc_user="remote@DOMAIN.TLD" -o imapc_password="PW" -o imapc_host="localhost" -o mail_prefetch_count=20 -o imapc_features="rfc822.size fetch-headers" sync -R -u local@DOMAIN.TLD imapc:

Seems to work and does nothing at the moment.

Deliver one message to local@DOMAIN.TLD (Subject Test3).

• doveadm -o imapc_user="remote@DOMAIN.TLD" -o imapc_password="PW" -o imapc_host="localhost" -o mail_prefetch_count=20 -o imapc_features="rfc822.size fetch-headers" sync -R -u local@DOMAIN.TLD imapc: Now Test1,2,3 are in both mailboxes (further runs do change nothing). Everything OK up the here.

Now deliver one messages to remote@DOMAIN.TLD (Test4) and delete one old message (Test3). Deliver two messages to local@DOMAIN.TLD (Subjects Test5 and Test6) and delete one message (Test2). In sum both mailboxes look like this: remote@DOMAIN.TLD has Test1,2,4 and local@DOMAIN.TLD has 1,3,5,6.

Now sync:

• doveadm -o imapc_user="remote@DOMAIN.TLD" -o imapc_password="PW" -o imapc_host="localhost" -o mail_prefetch_count=20 -o imapc_features="rfc822.size fetch-headers" sync -R -u local@DOMAIN.TLD imapc: dsync(local@DOMAIN.TLD): Warning: Mailbox changes caused a desync. You may want to run dsync again: 3 UIDs changed due to UID conflicts

Rerun again and see that mails start duplicating and deletings are not synced: remote@DOMAIN.TLD: Test1,2,4,3,5,6,5,6,6,5,3,4 (12 mails) and local@DOMAIN.TLD: 1,6,4,3,5,6,4,3,5,6,5 (11 mails)

When I re-run again I sometimes see the above error message again, mails keep duplicating in both mailboxes and the mailboxes are not synced at all.

Am I using doveadm sync wrongly? Is there a way to use "sync" directly w/o backup from the beginning (i.e., how to get rid of the error "Error: Backend didn't update mailbox Trash GUID").

Context: # 2.2.27 (c0f36b0): /etc/dovecot/dovecot.conf # Pigeonhole version 0.4.16 (fed8554) # OS: Linux 4.9.0-8-amd64 x86_64 Debian 9.8 imap_client_workarounds = delay-newmail

I can't upgrade to latest Dovecot right now. :(

-- Best regards, Sven Strickroth PGP key id F5A9D4C4 @ any key-server