We recently replaced our BorderManager 3.0 server with a BM3.7 server
new hardware).

Since that time, we have a client that is unable to email us. They
receive a Delivery Failure Report stating that "Router: Failed to
to SMTP host ABC.COM because: Server not responding".

I have SMTP filters in place allowing TCP port 25, and they exactly
the filters I was using on the old server.

We also have hundreds of emails coming in and going out.

But, for some reason, this one particular client cannot email us or
respond to an email that I send them.

I am using NAT (Static and Dynamic). The public address is bound via
Secondary IPAddress" and NATed to the private address.

I have Craig's book and have followed his filter setups.

Any idea why this would be happening ?