[Dovecot] Mail root to root and permissions problem

Hi all! I got a Debian with postfix-dovecot-spamassassin.

I got a non perfect installation: when an internal mail has been sent i got this error: <error> ex: from root@* to root@*. Command output: Can't open log file /var/log/dovecot.log: Permission denied </error> Operations like "dovecot: 2009-12-15 11:17:24 Warning: Killed with signal 15" are writen. It's a permission problem: dovecot.log is owned by "root" and grupped by "adm" (chmodded 640). Where is the problem? I'm really blind now!

Tx 4 suggestions! Bye, Antonello