Solve an attachment problem winmail.dat impossible to consult

This guide relates to files that are attached by your correspondent, and that are in the format winmail.dat when they arrive on your e-mail address managed by Infomaniak.

Preamble

This format winmail.dat is used when sending emails from Microsoft email software/clients such as Outlook to encapsulate formatting information, attachments and contacts in the message.
This can cause problems when recipients use other software/message clients that cannot properly interpret this format.

These files do not depend on the incoming or outgoing mail provider. This is a Microsoft specific problem, as indicated on their forums or on this page (in English).

Solve the problem of reading the attachment

Ask the sender to...

... return the message without using the format "winmail.dat", using a standard messaging format such as HTML or plain text format when sending messages and/or deactivating RTF formatting in Outlook settings before sending the email:
... disable sending in format RTF for recipients who are not on Microsoft email software/clients. To do this, it must open your contact form in its contact list, go to the "Mail Address" tab and select "Send text only".
... compress attachment into file zip standard before sending it.
... use another software to send its message, like Thunderbird e.g.

If you don't want to contact him again:

Use Websites and free online tools to decipher content and convert file "winmail.dat" in a more or less legible format...

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