I collected all the information I could about the messages, message types, senders, etc. and submitted the problem to Microsoft. (That was a fun one to describe with PSS.) After a few days of back and forth they determined:
"The issue seems to be caused by our Content Conversion engine setting a MAPI property on the message to tell Outlook to “hide” the attachments. The code only seems to do this if the MIME is formed where the Content-Disposition MIME header is set to “inline”. This is definitely a change in behavior from Exchange 2003…"
In English: A bug exists in Exchange 2007 when a message with ‘inline’ attachments is delivered. This bug causes Outlook 2003 to not display the message attachments correctly.
In my last correspondence with Microsoft they said that the code has been fixed for Exchange 2007 SP1 and a ‘backport to RTM’ has been accepted. Here’s to hoping they have a hot-fix soon.
- View the attachment in OWA: OWA correctly understands how Exchange 2007 stores attachment information for the message.
- Open the message and save the attachments: This one is a little counter-intuitive. Even though Outlook 2003 doesn’t display the attachments, it can still access them. By selecting the ‘Save Attachments’ option from the ‘File’ menu will allow you view and save the attachments.
- Forward the message: This gives you 2 options. 1) Forwarding the message to yourself will display the correct attachment information in the new message. 2) When composing the forwarded message you will see the attachments.
- Flag the message: ‘Flagging’ the message will cause Outlook 2003 to write information about the message to the Exchange database. This process will cause Outlook 2003 to set the appropriate information so that it displays attachments correctly.
- Upgrade to Outlook 2007
- Have the sender send ‘real attachments’: Since the problem only exists with ‘inline’ attachments the sender can change their mail client to send ‘real attachments’ and avoid future problems sending attachments to your organization. **Note: Mozilla mail clients send ‘inline’ attachments by default when composing HTML email. Instructions for changing this behavior can be found here.
Update: Update Rollup 3 for Exchange 2007 fixes the issue mentioned above.