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 email client doesn't support TNEF (most don't) you also recieve a winmail.dat 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 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

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

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