We utilize an external company to filter our email for spam and virus checking. However, we receive some direct emails, likely using our mail.companyname.com DNS name. That name is not in our MX table. We would like to prevent port 25 traffic coming from IP addresses not used by our external spam filtering company. We use a Cisco/Linksys WRT54G router that does not appear to allow use to easily configure this at the router level.
We utilize Symantec's Mail Security for Microsoft Exchange. I have read many posts on how to configure SBS 2011 (Exchange 2010) for limit traffic. But all the post appear to state that the default is 0.0.0.0 - 255.255.255.255. But that is not the case for our server. SMSME is catching these erroneous emails and deleting them based on a executable file detection rule.
Our Hub Transport Settings have the following:
192.168.1.1 is the default gateway and is not in the above listing.
I did not setup this server and do not have access to the original installer any more. It appears that SMSME is acting as a SMTP gateway as it is blocking the bad traffic. Don't know exactly how SMSME works so I don't know if the port 25 traffic first goes to SMSME and then to exchange or is integrated in some other fashion. It appears based on above that the listing may need to go somewhere else.
How can I accomplish this, given that SMSME is being used in addition to the outside service.