I am running a P.O.S. Exchange Server 5.5 (up for a couple of years). Some of my people have Outlook set up for both internal and external e-mail services. Recently, all of these people lost the outgoing mail capability. They could receive but not send. I was able to use the same settings on Outlook Express and had no problem on the SMTP side of things. Here's the error that I am getting: From: System Administrator Sent: Wednesday, December 12, 2007 6:07 AM To: 'abc@defg.com' Subject: Undeliverable: test Your message did not reach some or all of the intended recipients. Subject: test Sent: 12/12/2007 5:56 AM The following recipient(s) could not be reached: 'abc@defg.com' on 12/12/2007 6:07 AM No transport provider was available for delivery to this recipient. It is obvious (or is it?) that the Outlook client is trying to deliver the message through my internal mail server. I have not been able to find a configuration setting that would prevent this. By the way, I did set the Outlook client to try to deliver to an external e-mail account first. Any ideas?