I have recently had to change my email infrastructure so that all incoming email is passed through a relay at a different site, and then forwarded to me on a port other than 25. I have set up DNAT to reroute the odd port back to 25 so that the email relay / spam filter will process incoming email. Since this time, I have received a significantly increased amount of SPAM making it past the filters. Some messages are being stopped, so I don't believe that this is a configuration issue with the non-standard port. My best assumption is that this phenomenon is caused by UTM not rejecting email based on the sender's IP address, since it is now all coming from one IP. Is there a way to make UTM parse the headers and reject based on the IP address prior to my upstream relay?
If there isn't a way to do this presently, this would be a really good feature request for those of us with unfortunate email infrastructures such as this.
Any insight would be greatly appreciated. Thanks!
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