Sending is fine, internal domain and external.
I can Email, from another site, the domain and can see in the router log the SMTP request. A Network Trace shows the NIC with a source IP of the Email sender and it doing some SMTP stuff.
But I don't see the SMTP server receiving the Email nor Exchange getting it.
Could be the FireWall or even Exchange but I'm lost. Not really my area of expertise although I'm learning fast.
I have a MS paper on SMTP and Exchange to read ( 285 pages ) which seems the dogs but am 90% sure this is something very simple and a MCSE / MVP would laugh at my ignorance.
I'd be happy with that !