tnefDD is a program for Mac OS X that extracts attachments from TNEF format files. It is built as a modern OS X application with all the ease of use features like drag-and-drop that OS X user expect, and runs on Intel- and PowerPC-based Mac computers.
  1. Decodes TNEF format (winmail.dat) files
  2. Drag-and-drop operation
  3. Preserves attachment dates, making it easy to keep track of file versions
  4. Allows files to be opened with tnefDD, allowing the contents to be examined without copying the attachment to a new location
TNEF files
Microsoft e-mail programs written for Windows such as Outlook sometimes send e-mails in the Transport Neutral Encapsulation Format (TNEF). Most other e-mail programs, including Apple Mail and Microsoft Entourage, do not understand TNEF. If your e-mail program doesn't understand TNEF, instead of seeing the e-mail and/or attachment, you may only see an attachment named "winmail.dat" or "Part 1.2" that you cannot open. Also, sometimes you may receive a TNEF attachment with a generic name such as ATT00008.dat or ATT00005.eml instead.
While almost all attachments named "winmail.dat" are TNEF, you could receive non-TNEF attachments with names ending ".dat" or ".eml", or which are named or labeled "Part 1.2". In particular, AVG (an 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.
tnefDD decodes these attachments, and allows any attachments contained in them to be saved or opened.
tnefDD uses the core of the Mark Simpson's TNEF software (available at
System Requirements
  1. OS X 10.4.0 (Tiger) or later
tnefDD is free software, released under the GPL. However, if tnefDD helps you, you should donate to the project. You can donate by selecting the donate link on tnefDD’s project page at