How can I open winmail.dat or other .dat files?
Outlook users sending HTML emails with attachments often reach other users as an odd winmail.dat file. (Thanks, Microsoft!) I’ll show you some tips on how to open that attachment!
The perhaps easiest way to extract or view these sort of attachments is via the excellent website:
Max size allowed by winmaildat.com is 5MB, and if you do not want to upload / download any semi-private information, you can alternatively use a program listed below.
Alternatively, there are various dedicated programs which can open or extract those pesky .dat files!
For Windows, there are tons of free programs like Winmail Opener.
On OS X, check out tnef for OS X.
For Linux, tnef is available as well.
$ sudo apt-get install tnef
Then use tnef to extract the .dat file contents:
$ tnef winmail.dat