Fun with WINMAIL.DAT (not)

Someone told me of this problem when certain people reply to him, he does not see reply, but rather his own copy of the E-mail. (appears if the E-mail was resent back at him, but with recipient’s E-mail address.)

Investigating problem, I concluded this is bad implementation of Microsoft Outlook and also non-standard behavior of recipient’s E-mail system.

So here’s what happened. When he sent out his E-mail, it sends out winmail.dat, and that particular recipient was sending back original attachment, in this case winmail.dat back at sender when that person replies.

Winmail.dat, for those not familiar with it, is Transport Neutral Encapsulation Format which sounds like some sort of standard, but really is proprietary format used by Microsoft Outlook. When you send E-mail containing any RTF, the text of E-mail and its attachments are encoded into this format, and attached as winmail.dat.

It seems to be Microsoft Outlook reads winmail.dat higher priority than anything on the body of a E-mail, even when contents of these differs. Therefore, receiving original winmail.dat with reply caused Microsoft Outlook to display contents of winmail.dat (the original message) rather than contents of the body. (the reply)

Now, while I don’t think sending attachment with reply is a good thing, this same problem can potentially happen if someone forward E-mail with attachment, so I think Microsoft should be blamed on this case. In fact, this kind of problem is main reason I never use Microsoft Outlook. I had to use it at my work while ago, but I’d be trying to find some work around to not use it if I was forced to use one in future… Really, I never understood reason why they have to send E-mail in RTF at first hand, while there’s clear alternative of HTML for formatted E-mail. (Microsoft Outlook does support HTML E-mail, so why not dropping RTF?) Furthermore, encoding attachment into a proprietary format should be serious crime, really.

Searching for solution, I found out that KB958012 is a solution to this problem. This article explains the way to edit registry to disable Microsoft Outlook’s behavior of attaching winmail.dat. So here’s a question I want ask Microsoft. Why did you not include this option in options screen on the program, rather than forcing users search through your knowledge base to offer registry fix? Also, you should never ever allow winmail.dat on the internet E-mail. (I don’t want receive them either) What you’d be doing between users in your Exchange server is fair game; but at least use of winmail.dat should be whitelist basis.

By Hideki Saito

In the video game industry for for more than 15 years. Currently working for Nintendo of America Inc. as a Localization Engineer, developing the translation solutions.

2 replies on “Fun with WINMAIL.DAT (not)”

Comments are closed.