OK, if this just started for this one user then have you looked through the properties in his AD account yet to see if something was changed?

Nope. No changes.

Is he set up as a direct connection to exchange or is he set up as a POP3 account?

Direct connection to Exchange.

If you do a send/receive operation in his outlook does it complete successfully?

No.

Has he tried logging into another computer and sending from outlook?

Yes. When I had him login to the exchange web interface from another computer, he was able to send with no problems. Then I had him try it on his own computer and still no problems. Now it looks like this must be a problem with his install of Outlook (maybe it auto-updated over the weekend and there’s now some conflict). I plan on re-installing Outlook and seeing if that sorts it all out.

However, I’m still a bit concerned…. It turns out that this user is also not able to reach a shared folder that he has always been able to access, until last weekend. He is a member of a security group that has permission to access this folder. He also has explicit permission to access this folder. Finally, there’s another guy in the same security group who is having both of these same problems, sending e-mail from outlook and accessing the shared folder. As an extra hassle, there’s a relatively new user, in the same security group, who is able to access the shared folder, but is also not able to send from outlook….

This is an existing user who had no problems until yesterday. He’s had an account for at least the last year.