A Forum reader recently asked:
“We have an external service that handles all our antivirus and spam filtering for our email. I would like to set up the GWIA so it only will accept incoming email from this service, and it will only send outgoing email to that service.
What is the best way to accomplish this?”
And here’s the response from Joe Marton …
1. Edit the default class of service to deny SMTP inbound/outbound traffic.
2. Put in the appropriate exceptions for allowing traffic.
Or, if you don’t want to mess with GWIA, and assuming you have a firewall between your GWIA and the external service -
Configure the firewall to only allow 25/TCP traffic between the specific source and destination IPs.