My company has a external spam filtering service and just recently they asked that all of their customers lock down SMTP. What I need to do is block SMTP requests coming externally except for the IP addresses provided by my service provider.
So for example, if ihave to only allow requests on port 25 from the follwoing external ip addresses only, how would I do this:
10.32.248.12 subnet 255.255.255.248
10.32.248.252 subnet 255.255.255.248
Note the IPs are just for example purposes