If you get an email message with a winmail.dat attachment on your Mac
You can ignore winmail.dat attachments, which are related to the email app that the sender is using.
If you receive an email message sent from a Microsoft email app like Outlook or Microsoft Exchange, the message might include an attachment with "winmail.dat" in the name. The attachment doesn't appear in the Microsoft email app, but it does appear in Mail. In other email apps it might appear as a MIME section named "application/ms-tnef."
This happens when the sender composes a message that includes additional information about text attributes like a font, color, boldfacing, or underlining. To avoid seeing these attachments in the future, ask the sender to turn off the option in their email app that sends the message in Microsoft rich text format (or TNEF).
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