Winmail.dat – the simple fix and Microsoft’s complex answer

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What to do if recipients see a winmail.dat file? According to one Microsoft KB article there’s a patch required but there’s a much easier solution.

” Have you seen the KB article 958012 ? People complaining about winmail.dat has been a problem for me for many years – why is Microsoft only talking about this now and why such a difficult fix? ” — Jeremy W, Wisconsin.

Microsoft Knowledge Base article 958012 is quite new and based on what’s there does seem strange. First some background then we have a more elegant solution than the one given by Microsoft.


What is winmail.dat?

Winmail.dat is an email attachment you normally don’t see. It contains formatting information for RTF (rich-text format) messages sent by Outlook. The system used for this is called TNEF (Transport Neutral Encapsulation Format ) but despite the word ‘neutral’ it’s a proprietary Microsoft format. Because it’s an ‘in-house’ Microsoft format some non-MS email programs can’t convert the incoming message into a fully formatted message – the result is plain text plus a mysterious winmail.dat attachment.

These days RTF formatted messages have been largely replaced by HTML formatting because it’s more widely supported by email software. Outlook has supported HTML formatted emails for the last few versions and is much preferred over the proprietary Microsoft system.

The solution for Jeremy is to check the Outlook settings and make sure all messages are sent in HTML format.


Switching to HTML format

These days even Microsoft recognizes the superiority of HTML formatted messages. The default format is HTML and there’s even an option to convert RTF messages to HTML format when sending to Internet email addresses (as opposed to intra-organization recipients). Go to Tools | Options | Mail Format to see the default message format (should be HTML) then click on the Internet Format to see Outlook Rich Text option to convert messages.

Outlook - Rich text option - convert to HTML.jpg image from Winmail.dat - the simple fix and Microsoft

Most Outlook users (except perhaps those in large companies) would be using HTML formatted messages already without even knowing it. If you have people asking about winmail.dat messages from you then check your Outlook settings.


Individual Messages

You can control the formatting for individual messages and override the global setting in Outlook.

In Outlook 2007 this choice is on the Options tab:

Outlook 2007 - mail format for single message.jpg image from Winmail.dat - the simple fix and Microsoft

In Outlook 2003 the same choices are on the e-mail toolbar.

In normal practice you’d skip over the Rich Text option entirely. HTML is the best and most compatible choice for most purposes. Plain text is handy for special situations like messages to ‘Email to phone’ gateways.


Why the long answer?

Now back to KB 958012 which describes the broad problem of recipients seeing winmail.dat attachments sent from Outlook 2007. But the solution given is a complex one involving the 28 October 2008 hotfix plus adding a new registry entry.

As you can see above, the easier solution would seem to be switching to HTML format for outgoing messages.

Why this long answer in the KB article? Most likely there’s a more complex bug in Outlook 2007 that Microsoft doesn’t want to admit in detail.

The current wording of the KB article is misleading – people searching for a solution to the basic winmail.dat question would read that article and think the fix is far more complicated than it really is.

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