I use a mail filtering service that delivers mail to me via SMTP on standard port 25 on one of my 5 static external IP's. I wish to restrict this to their IP's only (they have two) and I am unsure on how to do so? As it stands now, anything on the net can talk to my mailserver and my logs are filling quickly with failed attempts as a result. Here's my setup and what I am trying to accomplish:
mail filtering service -> my public ip:25 -> internal mailserver at 10.0.10.2:25, deny everything inbound except traffic from the mail filtering service
I am thinking an ACL would fit the bill here, but unsure of how to implement.
Router is an 1811 with version 15.1(4)M3 IOS. WAN is on fa0, lan is on fa1.