Strange situation. Have a company with two physical sites connected via a point-to-point T1. On each end of the T1 are old Cisco 1602R routers. The problem is actually with Exchange servers failing to talk to each other properly. Site A is main office and Site B is branch office. Each site contains 1 Exchange server and the sites are supposed to talk over this p-t-p connection. I cannot use telnet to connect from site A to site B over port 25. I can however, connect from site B to site A over port 25.
Essentially, the communication between these Exchange servers is failing because messages cannot go from site A to site B, but can go from site B to site A.
The interesting thing is that I can use telnet from site A to site B using a different port, say 691 which is also used with Exchange and it works fine.
I can telnet into site B router and establish a telnet session to the Exchange server in site B.
The problem is router A. For some reason, it will not allow requests over port 25 to go through.