How do you backup e-mails for users when during the backup, they are deleting the e-mails from the Maildir (POPping) and at the same, and the SMTP server is also writing to it.
We're running Solaris on both the Dovecot and backup server. As backup software, we're using Veritas Netbackup. At this time, we just backup the Maildir data. I think the change that an open file is being backupped is very small, but besides that, our users mostly want to restore mail from a few days earlier.
On Solaris there is the 'fssnap' tool to make a snapshot of the filesystem. I could create a snapshot when the backup starts and delete it afterwards. An other solution could be mirroring the filesystem with Solaris Volume Manager. When the backup starts, break the mirror and restore it afterwards.
FreeBSD 5 also has a snapshot option for filesystems. 'dump' even has an option to create a snapshot just before it dumps that file system so you don't have to worry about changing files during the backup...
-philip