Cannot send messages with attachments

Question

I recently got a new 13" MacBook Pro with Snow Leopard. I setup Mail to work with our OWA Exchange Server and it works fine except for one major bug. I cannot send ANY messages that have attachments. Here's what I've tried so far to resolve the issue:
Tried a smaller attachment - no change
Tried a larger attachment - no change
Tried composing a new message - no change
Tried replying to a message - no change
Tried forwarding a message - no change
Tried different types of attachments (Word docs, pdfs, jpgs, etc) - no change
Updated to the OS to 10.6.1 - no change
What else can I try?

Answer 1

Right, forgot that part. It goes away for one second (as if the message has been sent), then comes back with this error:
Cannot send message using the server +(my smtp server settings)+. The Exchange 2007 connection to server +(our exchange server's ip address)+ failed. Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent.
Below that, I get a list of SMTP servers, but since I only use one account with Mail, its just the Exchange entry. There are three button across the bottom: Edit Message, Try Layer, and Try With Selected Server.
If I select my Exchange server and click Try With Selected Server, it comes right back with this same error.
If I click Try Later, it puts in the Outbox, but never sends it. I left a message in there for a day once and it eventually gave me this error again for that message.
If I click Edit Message, and remove the attachment, I'm able to send the message.
My guess is that Mail isn't encoding the attachments correctly, which means I'll have to wait for Apple to fix the bug.