Support TNEF

[jbremer]

See also https://sourceforge.net/p/ytnef/tnef-samples/1/, https://github.com/Yeraze/ytnef, and most importantly https://github.com/koodaamo/tnefparse.

[idiom]

Yeah, we could switch the code in the .msg unpacker to use tnefparse instead of parsing the OLE streams directly. I can take a look at this if you want.

[jbremer]

Eh, that would also be a possibility ;-) If you have some spare time that'd be great!