David A. Wheeler's Blog

Tue, 13 Jun 2006

How to read the mysterious Winmail.dat / Part 1.2 files (TNEF)

All too often nowadays people report that they “can’t open the attachment” of an email, because they only received a file named (typically) “Part 1.2” or “Winmail.dat”.

The basic problem is that in certain cases Microsoft Outlook uses a nonstandard extra packaging mechanism called “ms-tnef” or “tnef” when it sends email - typically when it sends attachments. What Outlook is supposed to do is simply use the industry standards (such as MIME and HTML) directly for attachments, but Outlook fails to do so and adds this other nonsense instead. The full name of the format is “Transport Neutral Encapsulation Format”, but that is a misleading name… it may be neutral on transport, but it obstructs reception.

Almost no other email reader can read this nonstandard format. Email clients that can’t (currently) read this format include Lotus Notes, Thunderbird / Netscape Mail, and Eudora. In fact, I’ve been told that even Microsoft’s own Outlook Express can’t read this format!

So take a look at my new article, Microsoft Outlook MS-TNEF handling (aka Winmail.dat or “Part 1.2” problem of unopenable email attachments). It gives you a brief explanation of the problem, and what to do about it, both from the sender view (how can I stop sending unopenable email?) and the receiver view (how can I read them anyway?).

path: /misc | Current Weblog | permanent link to this entry