Transport Neutral Encapsulation Format

Latest revision as of 10:52, 12 April 2024

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.

[edit] Identification

Such mail files start with signature bytes 0x78 0x9f 0x3e 0x22.

[edit] 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)
• Winmail Opener
• ytnef: TNEF command-line extractor
• XAD framework

[edit] Sample files

• http://libxad.cvs.sourceforge.net/viewvc/libxad/testfiles/MS-TNEF/
• https://github.com/koodaamo/tnefparse/tree/master/tests/examples
• dexvert samples — archive/tnef

[edit] Links and references

• Transport Neutral Encapsulation Format (Wikipedia)
• How to turn off winmail.dat attachments
• MS-TNEF format specifications