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Meaning of winmail.dat in mail attachment
This guide concerns files attached by your correspondent, which end up in the winmail.dat format when they arrive in your email address managed by Infomaniak.
These are in no way dependent on the incoming or outgoing email provider. It is a specific issue with Microsoft, as indicated on their support page or this page (in English).
What is winmail.dat?
The problem of attachments in "winmail.dat" format is quite common and can occur when sending emails from Microsoft email clients such as Outlook. The "winmail.dat" format is used to encapsulate formatting information, attachments, and contacts in the message. However, this can cause problems when recipients use other email clients that cannot interpret this format correctly.
Resolving the Attachment Reading Issue
Ask the sender to:
- Resend the message without using the "winmail.dat" format, using a standard email format such as HTML or plain text format 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 on Microsoft email clients. To do this, they should open your contact card in their address book, go to the "Email Address" tab, and select "Send using Plain Text only"
- Compress the attachment into a standard zip file before sending it
- Use another software to send their message, such as Thunderbird, for example
If you do not wish to contact them:
- Use websites and free online tools to decode the content and convert the "winmail.dat" file into a more or less readable format