To my understanding, when using mdbox, doveadm force-resync should be able to recover all the messages from the storage files alone, though of course losing all metadata except the initial delivery folder.

However, this does not seem to be the case. For me, force-resync creates only partial indices that lose messages. The message contents are of course still in the storage files, but dovecot just doesn't seem to be aware of some of them after recreating the indices.

Here is an example. I created a test mdbox by syncing a mailing list folder from a mbox location:

$ dsync -m haskell-cafe backup mdbox:~/dbox

Then I switched the location to the new mdbox:

$ /usr/sbin/dovecot -n # 2.0.15: /etc/dovecot/dovecot.conf # OS: Linux 3.2.0-0.bpo.1-amd64 x86_64 Debian wheezy/sid mail_fsync = never mail_location = mdbox:~/dbox mail_plugins = zlib passdb { driver = pam } plugin { sieve = ~/etc/sieve/dovecot.sieve sieve_dir = ~/etc/sieve zlib_save = bz2 zlib_save_level = 9 } protocols = " imap" ssl_cert =

Then I checked the number of messages we had in the new location:

$ doveadm search all | wc 93236 186472 3625098

This was indeed the correct number, so the sync was fine:

$ grep -c '^From .*..:..:.. ....$' ../mbox/haskell-cafe 93237

Then I removed all the indices and rebuilt them:

$ mkdir bak $ mv mailboxes bak $ mv storage/dovecot.map.index* bak/ $ doveadm force-resync inbox doveadm(la): Warning: mdbox /home/la/dbox/storage: rebuilding indexes

And what have we now:

$ doveadm search all | wc 43864 87728 1699590

Somehow dovecot lost over half of the messages!

This is really worrisome. It should always be possible to extract the plain mail content out from the storage, but currently it only _looks_ like it is possible: you get a problem in the indices, rebuild them, and then later migrate somewhere else. If you don't notice that you are missing mails, you may then eventually destroy the original mdbox storage files, thinking that their content is now safely elsewhere, when it really isn't.

Lauri