Many ISPs do this. I know mine, Verizon, does as well for "home" internet connections. This is to get you to pay more money for a business-class connection, where port 25 isn't blocked.
As far as email proxy scanning, maybe a dnat rule to convert anything incoming from port 2525 to port 25 may work. Others may have better or different ideas to share.
__________________ ACE v8/SCA v9.3
...still have a v5 install disk in a box somewhere.
Any -> {port 2525} -> External (Address) : DNAT to SMTP
When traffic hits an Astaro interface, the first things considered are DNATs, then Proxies, then explicit routes and packet filter rules and, finally, SNATs are applied.
Cheers - Bob
Sophos UTM Community Moderator Sophos Certified Architect - UTM Sophos Certified Engineer - XG Gold Solution Partner since 2005
Comcast is often good about leaving 25 open, but they'll shut it down if they see a lot of traffic. If your mail volume is low, you may be able to get it opened by simply asking. (Try the Comcast folks on Twitter if you use it, they are usually easier to deal with than the regular support team).
