How to Fix Recipients Receiving winmail.dat files from Outlook 365

I’ve had an ongoing problem with my email recipients receiving winmail.dat files when I send them emails from Outlook using my Microsoft 365 email account and I’ve tried multiple ways of fixing the problem. I read that the problem is caused by Outlook sending emails in Rich Text Format (RTF). It includes the winmail.dat file invisibly to help preserve the formatting, but non-Outlook email clients can’t interpret the file, so all they see is the winmail.dat file.

Numerous sources said to go to Outlook>File>Options>Mail and change Compose messages in this format: HTML.

Outlook Options window

It didn’t help. I tried modifying the recipient’s entry in the Personal Address Book, but I couldn’t find that option, I assume because the latest version of Outlook for Microsoft 365 did away with it. I finally gave up and called Microsoft support and got an answer. This finally took care of my problem.

Login to your Office 365 admin account at and then click on Admin centers on the left sidebar navigation.

Microsoft Admin Center sidebar navigation - way to fix winmail.dat issue

Click on Admin centers. (I know, it seems redundant doesn’t it?) Next, click on Exchange under Admin centers.

Click on Exchange

Click on rules under the mail flow section.

mail flow rules

Click on remote domains, then click on the pencil icon to edit the Default rule.

click on remote domains

Finally, on the Remote Domain screen, click on Never under Use rich-text format. Click the Save button and your winmail.dat troubles are over!

Settings to change to eliminate winmail.dat files

I was told that if you wanted to change this setting for just one domain, you could do that too. Just click the + to add a new rule instead of the pencil to edit the default.


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Michele Caldwell

Generalist. Conservative. Born again lover of Jesus. Night person. Computer geek. Outgoing introvert. Lover of road trips. Singer. Cancer survivor. Happy. Friend.


  1. Siobhan Casey on September 26, 2019 at 8:52 am

    Thank you, thank you, thank you. I’ve been trying to fix this issue for months!

  2. Kent on October 22, 2019 at 1:26 pm

    This definitely works. Thank you so much! God Bless you.

  3. Jeffrey A Franklin on November 11, 2019 at 11:38 am

    Thank you!

  4. Jessica Knight on February 6, 2020 at 12:25 pm

    Worked for us as well. Many thanks!!

  5. Michelle on March 31, 2020 at 11:54 am

    Thank you! Thank you! Thank You! So thankful to finally find something that worked for me after so many different go arounds!

  6. Bruce on July 14, 2020 at 4:20 pm

    This fix was amazing! Thank you!

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