If you configure the SMTP Proxy, you don't need a Packet Filter rule for SMTP. Unless you configure the SMTP Proxy to relay for something, it won't relay.
On the 'Relaying' tab, we normally only put internal mail servers into 'Host-based relay'. If you put 'Any' or 'Internet' in there, you will have created an open relay.
Cheers - Bob
Sophos UTM Community Moderator Sophos Certified Architect - UTM Sophos Certified Engineer - XG Gold Solution Partner since 2005
