Thunderbird - winmail.dat

LookOut is a plugin which allows Thunderbird (and SeaMonkey) to interface with Microsoft's mail tools by decoding metadata and attachments encapsulated/embedded in a TNEF encoded attachment (aka winmail.dat). The TNEF decoding engine was inspired (with permission) by the TNEF project. LookOut has a full MAPI decoder and the ability to transcode some of those properties to iCalendar (ics) and vCard (vcf) formats. As an option all MAPI properties within a email can be viewed so other types of information can be deciphered.

https://addons.thunderbird.net/en-US/thunderbird/addon/lookout-fix-version/