Problem with Sophos together with my own spam filter

Question

Hi. 
 
 I'm running SFOS 19.0.1 and are currently migrating my mail. We have our own antispam (Xeams) placed in our DMZ and have no subscription for Sophos antispam solution. I really need some guidance on howto make Sophos work with an existing antispam solution. We do not understand if we should use the SMTP relay somehow. Just setting up NAT rules to forward port 25 to our antispam does not work. When we try to connect to port 25 on WAN side (using telnet) we do not get any answer. 
 It seams that there is some magic going on with implicit behavior when we use port 25. 
 I should also mention that the public IP for incoming mail is set as an alias in Sophos. 
 
 Any tips are appreciated 
 Thanks! 
 /Conny

emmosophos · Answer

Hello Conny, 
 Thank you for contacting the Sophos Community. 
 For configuration-related issues, I would recommend you to reach out to your Sales Engineer or Professional Services, so they can help you setup your domain. 
 For this, however, you can create a DNAT Firewall rule on the Sophos Firewall to pass traffic down to your Email Server on Ports 25, 587, 465 and probably 995,143, 110 
 The Firewall Rule would look like this: 
 
 and the NAT is like this: 
 Note: the Email Server entry under Translated Destination (DNAT) is the IP of your Email Server.

Or you can use the Sophos Assistant, which should guide you trough the DNAT configuration.