I am wondering if the SMTP (port 25) is being blocked by default on the ASA 5510 Firewall. The reason I am asking is that when one of my exchange server tried to forward emails to the exchange inside the ASA 5510, the connections will always be dropped. I tried the packet tracer and it always say that the packet was dropped and the access rules that dropped it is the Implicit IP deny all rule.
I had performed a NAT on the 5510 for the exchange server and still the traffic does not comes in for Port 25 only. Specific rules had also been added to allow TCP/25 through but still the same problem. I wonder if there is an "inspection" on SMTP/25 which caused the problem? If not, how can I overcome this problem so that connections between the two exchange servers will talk to one another?
Many thanks for any suggestions,