Over the past couple of weeks we have been researching some reports regarding encryption not handling attachments correctly. During the process, the error that kept printing on the back end processing was ““Content-Type: application/ms-tnef; name=”winmail.dat” Content-Transfer-Encoding: base64””. If Outlook sends a message using the RTF format (which is not very common outside Outlook) for bold text and other text enhancements, it includes the formatting commands in the winmail.dat file. Receiving email clients that do not understand the code therein display it as a stale attachment. To make matters worse, Outlook may also pack other, regular file attachments in the winmail.dat file. That’s the bad news, the good news is that fix is a piece of cake.

In Outlook 2010 you go through File, then Options and check the box below:


In Outlook 2007 you go through Tools, then Options:


1. Go to the Mail Format tab.

2. Under Compose in this message format:, make sure either HTML or Plain Text is selected.

3. Click Internet Format.

4. Make sure either Convert to Plain Text format or Convert to HTML format is selected under When sending Outlook Rich Text messages to Internet recipients, use this format:

5. Ok to submit.

Carlos Lascano
VP Support Services, ExchangeDefender
(877) 546-0316 x737