I've just received a New Message from Directadmin, entitled as "Backup Abort: A hard link was found under User username's path". And I've seen a list of files within /home/username/imap/ directory which seem to be hardlinks.
A quick investigation and here is what I've found.
By default dovecot when copying a message, does it with hard links whenever possible. Dovecot's wiki says that, this makes the performance much better, and it's unlikely to have any side effects. Only reason to disable this is if you're using a filesystem where hard links are slow (e.g. HFS+).
The behavior can be changed by the following directive (maildir_copy_with_hardlinks) set to no:
Note, even if you disable the usage of hardlinks in /etc/dovecot.conf, that is still up to you to remove the existing hardlinks.
Please check this link for more details: http://wiki2.dovecot.org/MailLocation/Maildir
Since Directadmin finds the hardlinks it terminates a backup process of an user account, though still the backup of the account with the recent date might exist (at least in my particular case, but directadmin help pages say the opposite), but it misses the imap folder. Other accounts which don't have hardlinks should be added to backups without an issue. Add the following line into /usr/local/directadmin/conf/directadmin.conf to disable the check (which is probably not that secure):
And restart directadmin.
It's said on the Directadmin official help pages:
Before all account backups are created by DA, a check will be done on the User's backup path. For any hard link found, DA will notify all Admins on the box, even if the backup is being created by the end-User. As well, the creation of that backup file will be aborted.
Please check this article for more details: http://www.directadmin.com/features.php?id=1061
Whether or not to disable the check you should decide yourself. If you are the only user on the server, and keep your CMS updated and secured, then you probably can disable the check, and leave Dovecot with enabled by default maildir_copy_with_hardlinks.
It has been just announced by Directadmin developers, that the next release (1.433) will fix it.
DirectAdmin 1.43.3 has been released.