I was able to get a message through, but I had to cripple my mailserver to do it
The problem seems to be with our oddball network configuration.
Our interface with the outside world is a little unusual:
Cisco Router ->
Mikrotik Router ->
Subnet with mailserver
Subnet with fileserver
The computer with the Mikrotik software router has three NICs - one to the Cisco, one to the mailserver, and one to the fileserver and the rest of our internal network.
The Mikrotik router has a NAT rule to change the IP address by which the world knows our mailserver (e.g., A.B.C.D) to the address by which our internal network knows it (10.10.10.1). There is no similar NAT rule for traffic originating in the internal network.
When the fileserver sends an email to firstname.lastname@example.org
, I want it to be smart enough to send it to email@example.com. However, it tries to send it to bill@A.B.C.D. I cannot traceroute A.B.C.D from my fileserver - it hangs at the Cisco Router. I am not sure why, but I think it has to do with my NAT rules.
I temporarily added two NAT rules to the Mikrotik so that packets originating in the internal network and addressed to A.B.C.D are NAT'd to 10.10.10.1, and packets from the mailserver to the internal network are NAT'd from 10.10.10.1 to A.B.C.D. I was able to send the email (yay!), but it of course broke every computer that tried to connect to the mailserver using 10.10.10.1. The mailserver's NAT'd response would say it was A.B.C.D when PC was expecting 10.10.10.1, and connection could not be established.
So I seem to have two approaches for fixing the problem. (1) get my fileserver to resolve foo.com as 10.10.10.1, or (2) change all hundred-odd computers on my internal network to POP3 over using mailhost of A.B.C.D instead of 10.10.10.1.
Not sure if (1) is possible, but it sure looks easier.
Thanks again if you got this far