This problem took awhile to figure out, so I figured it might be helpful to post it.
Setting up incoming email for SharePoint 2010 Enterprise, as instructed by TechNet: http://technet.microsoft.com/en-us/library/cc262947.aspx. Configured SMTP service, set up the Exchange connector, and configured incoming email settings in SharePoint 2010 Central Administration. Created a test document library, configured it with an email alias, and tried sending a test email. Test email went through, so we’re looking good.
Next, sending an email message with an attachment (the library is configured to save both the email message and the attachment). The email message arrives without any issues, and the attachment shows up as well.
Next, another user is going to send a test message with an attachment to the same library. His email message goes through, but no attachment! What’s going on?
In Notepad I opened the message that I sent with an attachment (which worked) and compared it to the message that did not work.
In the attachment section, we’re finding the following:
My email attachment – Works in SharePoint
Content-Type: text/plain; name=”test file.txt”
Content-Description: test file.txt
Content-Disposition: attachment; filename=”test file.txt”; size=9;
creation-date=”Sat, 03 Nov 2012 04:19:07 GMT”;
modification-date=”Sat, 03 Nov 2012 04:19:07 GMT”
The other user’s email attachment – does NOT work with SharePoint incoming email.
Content-Disposition: attachment; filename=”winmail.dat”
Content-Type: application/ms-tnef; name=”winmail.dat”
Notice the difference in the Content-Type fields – mine is text/plain, while his is application/ms-tnef.
We both specified Plain Text message format in Outlook before sending the messages. So what’s causing the difference in attachment format?
After some research on the topic, we’ve stumbled upon this Technet forum thread:
The answer in this thread resolved our problem – changing the properties on the remote SMTP domain in Exchange to never use Rich Text format for messages allowed the attachments to work for all users.