Winmail.dat attachments

This article was written for Thunderbird but also applies to Mozilla Suite / SeaMonkey (though some menu sequences may differ).

Outlook uses the Transport Neutral Encapsulation Format (TNEF) to send messages with Rich Text Format (RTF) formatting. If your e-mail client doesn't support TNEF (most don't) you may also recieve a winmail.dat or a "Part 1.2" attachment. Sometimes you may receive an attachment with a generic name such as ATT00008.dat or ATT00005.eml instead. You can configure Thunderbird to use one of the programs below to open the application/ms-tnef attachment.

• Fentun Win9X, NT, and Win2K but not Windows XP

• AkeeSoft WMViewer Windows 95X though Windows Server 2003

• Winmail Opener Windows 95X though Windows Server 2003

• TNEF Linux

• TNEF's Enough OS9 and OSX

Note that AVG (a anti-virus program) can also add a "Part 1.2" attachment that contains the same information about the message having been scanned for viruses that it adds to end of the message body.

The sender can avoid sending a winmail.dat file by turning off TNEF in Outlook.

1. On the "Tools" menu, click "Options", and then click the "Mail Format" tab.
2. In the "Send in this message format" list, click "Plain Text" or "HTML", and then click "OK".

External links

• Microsoft article on TNEF

• Microsoft article on how to prevent winmail.dat attachments from being sent to Internet users