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Winmail.dat and Other Annoying Attachments

Have you ever received email attachments named "winmail.dat" or "Part 1.2.1," or similarly named, inaccessible documents? What's up? Read on.

Microsoft Outlook allows its users to send mail in a non-standard rich text format known as TNEF. As a matter of fact, Outlook users aren't explicitly told that they're sending TNEF, so they have no idea they're causing you any problem. As far as they're concerned, they're creating a more readable text message for you. You, on the other hand, receive an email message with one or more mysterious attachments that you can't seem to open with any application you have.

The attachments are named "winmail.dat" or "Part 1.2.1" or something similar, and usually contain a TNEF formatted version of the message you received as plain text. Occasionally, however, there will be a document that is included in the winmail.dat file that you have no way to open.

So, what can you do when you receive one of these attachments? Here are some suggestions that may help.


  • Download the LookOut add-on for Thunderbird LookOut will create an attachment that you can open in MS Word or OpenOffice. To install it, go to Download, save it in a file, and in Thunderbird use Tools-Extensions-Install to install the file. When you receive a TNEF attachment, it will be put into a .rtf file that contains the text for the attachment.
  • Let the sender know it's a problem Chances are that you're not the only one having a problem reading the sender's emails. You can point them to information on how to disable the sending of TNEF at
  • Find out more If you'd like to find out more about TNEF, and find other utilities to help decode the files, check out and


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