We have a couple of in-house C/C++ applications that issue SMTP commands to send emails out. They basically issue the following over a socket:

HELO domain.com
MAIL FROM: user@domain.com
RCPT TO: user@externaldomain.com
test test test

This has worked fine in the past and no longer functions correctly at all. The hosts on our internal network are allowed to relay (based on the client IP address)

Whenever we try to send out this way now, the message somehow ends up coming INBOUND as if it was created outside the network entirely from internal user destined for a user outside our network.

I'm not sure why an outbound message created this way would end up in the in-bound email stream.

I've also tested this with telnet internally on port 25 and got the same results.

Any ideas?

Thanks, everyone.
Joe Jenkins