Transport Neutral Encapsulation Format

File Format
Name	Transport Neutral Encapsulation Format
Ontology	Electronic File Formats E-Mail, newsgroups, and forums Transport Neutral Encapsulation Format
Extension(s)	.dat, .tnef
MIME Type(s)	application/vnd.ms-tnef

Transport Neutral Encapsulation Format (TNEF) is a proprietary format used by Microsoft mail software to encode attachments and rich text, instead of more standards-compliant methods such as MIME.

It is usually implemented as an attachment called winmail.dat or win.dat, which Microsoft programs know what to do with, but is a useless and confusing attachment to everybody else (unless they use one of several programs and plugins that have been devised to help non-MS-ers cope with it). When saved elsewhere as archives or samples, sometimes the .tnef file extension is used.

Software

• Fentun: Freeware Windows program to decode this attachment
• TNEF: An open source TNEF decoder utility
• Lookout: Thunderbird addon to read TNEF (based on the above TNEF decoder utility)

Sample files

• http://libxad.cvs.sourceforge.net/viewvc/libxad/testfiles/MS-TNEF/

Links and references

• Transport Neutral Encapsulation Format (Wikipedia)
• How to turn off winmail.dat attachments