A proprietary data file generated by Microsoft Outlook when messages are sent using the "rich text" mail format setting. This file not actually a "*.RTF" file, but is encoded using the "Transport Neutral Encapsulation Format," aka TNEF, pronounced "tee-neff." Any formatting codes such as bold, italics, font choices, and the like are kept in this file, which in and of itself is not too obnoxious, because you can still see the text of the message, stored in a separate plain text file. Assuming the recipient is using Outlook, this whole process is transparent and no plain text or WINMAIL.DAT file is present. However, users of Internet e-mail services or other clients such as Eudora and Outlook Express will not be able to see your formatting, and may be confused by the presence of this strange, seemingly generic file.

This might seem like a rather innocuous problem, but the real pain-in-the-ass is that any file attachments sent in a rich text message are buried in this proprietary file as well. Let's say, for example, that you are applying for a job and are sending your resume using Outlook, using the rich text format. Granted, much of the industry uses Outlook, but if they happen to be using Eudora, all they get is this WINMAIL.DAT file. Your potential future employer is then forced to contact you and let you know that they've got this useless data file, assuming they don't immediately consider you to be technically inept and ignore your e-mail entirely in light of the fact that there are plenty of other perfectly readable e-mails to parse through.

If you happen to receive a very important attachment that comes by way of WINMAIL.DAT, do not fret. You have some options:

  • Have the original sender change their mail format to plain text, or alternately, they can alter their contacts file so that messages sent to you are always in plain text. Then re-send.
  • Do a search for "winmail.dat decoder" on google or any other search engine and you are bound to find at least five different programs that will allow you to access this data.

There are a couple of things I'm not positive on, perhaps a fellow noder might clue me in:

  • Does this happen when using the HTML format? Everything I've read insists on using plain text, so I'm assuming it does. I'd test this myself, but can't at the time, being that I'm at work and we can't send external e-mails via Outlook.
  • Does Lotus Notes have the capability to decode these messages? Everything I've read so far only discusses problems with Eudora and services like Yahoo! and Hotmail.
  • Does MSN's e-mail service have this problem? You'd think Microsoft would be intelligent enough to implement such a decoder for their own service.

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