[Dovecot] Problem with dovecot delivery (version 2.0.7)

Hi!

I've been having an issue with dovecot since yesterday and can't figure it out.

All my users can send mail without any problem but all incomming mail are deffered. Here is the log from postfix complaining the mail has been deferred:

Nov 9 23:35:51 www postfix/pipe[50019]: A20EB145FC2C: to=, relay=dovecot, delay=819, delays=819/0.01/0/0.01, dsn=4.3.0, status=deferred (temporary failure)

And here is the log from dovecot complaining it can't complete the operation /var/log/dovecot-deliver.log:

Nov 09 23:35:51 lda(EMAIL REMOVED FOR PRIVACY): Fatal: setresgid(6(mail),6(mail),6(mail)) failed with euid=143(dovecot): Operation not permitted

If anyone could help me, it would be much appreciated!

Thanks!