GPGMail: winmail.dat support

Dieter's Avatar


09 Apr, 2018 10:15 AM

today I was surprised to hear that one of our employees was able to open a mail containing a winmail.dat file which again contained an gpg encrypted email, without the need of external program or plugin ( TNEF enough, or Letter Opener).

This obviously means that GPG-tools can handle winmail.dat files out of the box ?

If so, I'm even more surprised that another employee, who has received the same mail and is using the latest "stable" version of GPGtools, was not able to read the mail. She had to open the winmail.dat attachment with "TNEF's enough" and then save the attachment as .EML file, which then could be opened and decrypted using

So the question is: is that supposed to work without the help of en external program ?


  1. Support Staff 1 Posted by Luke Le on 10 Apr, 2018 12:43 AM

    Luke Le's Avatar

    Hi Dieter,

    that was probably more luck than anything else.
    GPGMail currently has only minimal highly experimental support for PGP data in winmail.dat files built-in. It also depends on what macOS version you are using GPGMail on. For example on macOS High Sierra, it will not try to handle winmail.dat at all if Letter Opener is installed, since we have yet to find a better way for the two plugins to co-exist on High Sierra.

    We only added some support for winmail.dat/TNEF in the first place, because for some reason Microsoft Exchange Server, sometimes decides to pack an entire PGP/MIME message into a winmail.dat file. If you have such winmail.dat and you could share them for testing/debugging purposes, that would be interesting.

    Generally for winmail.dat I recommend using Letter Opener. Full disclosure, the developer is a good friend of mine hence I know all the hassles he has to deal with when it comes to winmail.dat/TNEF

  2. Steve closed this discussion on 18 Jul, 2018 02:16 PM.

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