Solve an issue with a winmail.dat attachment that cannot be viewed

This guide concerns files attached by your correspondent that arrive in winmail.dat format to your Infomaniak-managed email address.

Preamble

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

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

Solving the attachment reading issue

Ask the sender to…

… resend the message without using the "winmail.dat" format, by using a standard email format such as HTML or plain text when sending messages and/or disabling RTF formatting in Outlook settings before sending the email:
… disable sending in RTF format for recipients who are not using Microsoft mail software. To do this, they must open your contact card in their contact list, go to the "Email Address" tab, and select "Send in plain text only".
… compress the attachment into a standard zip file before sending it.
… use another software to send his message, such as Thunderbird for example.

If you do not wish to contact them again:

Use websites and free online tools to decrypt the content and convert the "winmail.dat" file into a more or less readable format…

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