I recently did a migration from one VPS to another by simple backup and restore. Great process that went smoother than expected. Just one thing I noticed: sieve filters in email accounts seem to not be backed up or restored.
This might be something that could easily be implemented in a future release.
@NCKNE Which app did you use the sieve filters in. Often, the filter in one app is not visible in another!
The sieve filters are located at
/home/yellowtent/boxdata/mail/vmail/<mailbox>/sieve. Can you check if they are there on the filesystem atleast?