Binary package “ktnef” in ubuntu jammy
Viewer for mail attachments using TNEF format
The TNEF File Viewer allows one to handle easily mail attachments using
the TNEF format. Those attachments are usually found in mails coming from
Microsoft mail servers and embed the mail properties as well as the actual
attachments.
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An attachment in TNEF format is most often named winmail.dat or win.dat.