Got a weird one. I have one user in my domain of several hundred who is experiencing this problem. His account can send and receive just fine when using OWA, but he can only receive (not send) when using Outlook. All traffic is for internal recipients.
I have tried setting him up w/ a fresh install of Outlook, I've tried using a new computer w/ a fresh install of Outlook as well. I have likewise tried removing the exchange features from his account and re-adding them (he's a new user, so losing the MB wasn't a big hit). No joy on any of this.
On the Exchange server, I see the messages in the queue that's got the fully qualified name of the primary exchange server, and they're all listed as state of Retry.