> Mails are collected by fethcmail (as daemon using /etc/fetchmail.rc) > > > So, you aren't going to receive any email on your VPS, then you should configure inet_interfaces to listen only your VPN IP http://www.postfix.org/postconf.5.html#inet_interfaces
You can even listen to the submission port (instead of SMTP/25) and close 25 with a firewall.
