Upgrading to Exchange 2007 seems to change the behavior of sending
SMTP e-mail through Outlook 2007.

Using Outlook 2003, I could specific an outbound SMTP server and enter
the credentials.

Upgrading to Outlook 2007 changes this. Now I get constant prompts for
entering my credentials.

After playing around with the settings, the way I got it to work was
to uncheck 'My outgoing server (SMTP) requires authentication".

After doing that, I can send/receive e-mail without a problem.

Does anyone have an idea why that is?