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Outlook can sometimes reformat attachments to 'winmail.dat'. This is most often when the email client is sending out emails that contain Rich Text such as blog, italics, etc. The formatting is stored in the winmail.dat file. The recipient email clients may store that data as an attachment. Other normal file attachments are also stored as winmail.dat files as well. Below is a quick guide on how to stop this from happening.

How to prevent winmail.dat file types in Outlook

  1. Open up your Outlook email client.
  2. Click on File located in the upper toolbar.
  3. Select the Options setting.
  4. From here, select the Mail category.
  5. Now, under Compose messages, you want to ensure the HTML or Plain Text option is selected for the Compose messages in this format.
  6. Next, underMessage format, set When sending messages in Rich text format to Internet recipients to Convert to HTML format or Plain Test format
  7. Click OK to finish.
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n/a Points
2019-05-01 2:19 pm

How does this work with sending appoitnment calendar events from Outlook to an Android Samsung Galaxy?  We can't get the winmail.dat to convert when sending appointment to the android.  Any help is greatly appreciated!

42,943 Points
2019-05-01 3:46 pm
This appears to have been addressed in the Samsung Community forums. Check out this post. If you continue to have problems, I would recommend speaking with Samsung support.
n/a Points
2019-03-20 6:07 pm

thanks a lot, i was looking for weeks to get that solved, and this worked !!!

n/a Points
2018-03-03 12:43 am

I was sending a file from my laptop to my phone so I could print it.  Had the windat issue so I first deleted the newly downloaded windat file opener app from my Android phone.  That didn't make a difference.

Then I deleted myself from the autofill application in Outlook 2013 on my laptop and that worked. 

I'm inclined to think the windat app on my phone somehow affected the process but I can't imagine how.  I only know that the windat attachment issue started appearing after I downloaded the windat app on my phone.  I say that because I created a word doc on my phone and sent it to my laptop for storage -- because I don't feel like using Google Drive or anybody's else Drive...tired of feeling invaded by Drives :(  So I'm guessing the windat app on my phone somehow infected Outlook 2013 on my laptop.

Hope this added detail helps others answer the Why?


n/a Points
2018-04-16 3:08 pm

Joyfully, I report the problem is easy to fix. This seems to be an outlook issue on the windows sending device, not the Mac receiving device. The recipients address in outlook auto-fill somehow gets corrupted. The issue occured for me when emailing a PDF attachment from a windows PC running outlook 2016 to a Mac computer running outlook 2016. The PC emails out a PDF formatted attachment, the Mac receives a winmail.dat formatted attachment. The fix is to resend the PC's outlook email attachment, but first delete the recipients autofilled email address. Manually type-in the recipients email address into the 'To' portion of the email, then send the email. For years, I have used multiple outlook versions on Windows and Macs, and I have never encountered this issue before. Strange occurance, but easily remedied.

n/a Points
2018-12-04 1:03 pm

It worked!!


Your suggestion to physically type in the complete email address (on the Sender's computer) instead of letting it autofill by typing the first couple letters worked!

I typed the entire address and even added an extra letter then deleted it - myname@thatplace.coms and sent and the attachment went through properly.

After that using the autofill as normal worked again. So weird. Thanks for the suggestion!

n/a Points
2018-12-04 10:44 pm

Problem solved. Thank you sooooooo much. I was able to fix this by deleting the the recipients autofilled email address. I really appreciate it.

n/a Points
2019-01-28 2:00 pm

I had the same problem and did that typing in the address manually and, weird as it seems, it worked.

Then the auto fill was fine.

Who on earth managed to come up with that solution well done - I don't think I would ever have even tried that but thank you so much.

n/a Points
2019-03-12 8:48 am

Finally a solution that actually works. 



n/a Points
2019-04-10 5:48 am

Thank WORKED......

n/a Points
2017-09-17 3:46 pm

My email attachments to two contacts all of a sudden were being received as winmail.dat on their iPhones.  Deleting the contacts, and then readding them solves this problem.

n/a Points
2017-07-26 9:28 am

trie what the post said.  no luck.  i deleted the contact, deleted the autofill entry.  re-added the contact   this worked.  no idea why

n/a Points
2017-05-23 7:06 pm

So I am the one with Outlook and my messages, only very recently, have started to arrive with any PDF in windat mail format???  I checked the settings and I already have HTML default and convert to HTML format set....  so this clearly is not the solution.  

Any other ideas....  as this only really started happening more recently it would suggest that some update on either end is triggering this issue!


Thanks in advance for any help!


42,943 Points
2017-05-24 1:13 pm
Hello Rachel,

This appears to be a Microsoft setting issue. Check out this post in the Microsoft Support Forums.

If you have any further questions or comments, please let us know.

Arnel C.
n/a Points
2016-11-14 1:59 pm


Does not work for Outlook 2016. Cheers Microsft, bunch of w****s. Only works with new email addresses.


About time Microsoft put an option in Outlook "Send winmail.dat Yes/No!!!!"

n/a Points
2016-09-16 3:42 pm

I am having a similar issue.  However, it is not isolated to just Rich Text.

I have a client with Outlook 2013 attempting to send emails to another client with Apple Mail 8.2.

I have sent an email with a pdf and word attachment in all three formats (Rich Text, HTML, and Plain Text).  All three emails show up on client B's Apple machine as an email message with a winmail.dat attachment.

I tried sending the same email from my machine running Outlook 2016 in HTML to Client B on the Apple machine and was able to see the email correctly with the attachments showing.

I have tried changing the settings for all three types from Client A's machine.

Spinning my wheels now.





42,943 Points
2016-09-16 3:51 pm
Hello Joshua,

If the problem was not resolved by the provided Micorosoft post. Then I would recommend contacting Microsoft for further help with that issue. They are the authors of this software and can help provide a working solution

If you have any further questions or comments, please let us know.

Arnel C.
n/a Points
2017-08-05 3:30 pm

Just WONDERFUL advice. Thank you SO much.

n/a Points
2017-07-25 9:35 pm

Josh, any luck on this? I have the exact same problem.

42,943 Points
2017-07-26 7:36 am
Hello Peter,

If the above solution ( in the article) is not working, then I highly recommend contacting Microsoft support on the issue as it is related to the application.

If you have any further questions, please let us know.

Kindest regards,
Arnel C.
n/a Points
2016-07-21 8:12 am


how to remove winmail.dat from outlook 2013 

13,821 Points
2016-07-21 8:37 am
The resolution is described in this article from Microsoft:
n/a Points
2017-01-02 5:36 pm

Doesn't work with outlook 2013 

n/a Points
2015-06-13 9:23 am

The instructions do not apply to me and wouldn't work.

I already have my emails sent in HTML and the convert box in step 6 was already checked.

The problem happens anyway.

However, if I send the email in text mode, the PDF file is not converted to a dat file.

Text mode appears to be the only workaround. → too bad Bill Gates doesn't use some of his billions to fix stuff like this.

n/a Points
2015-11-03 12:28 pm

You realize Bill Gates doesn't run MS anymore, right? I'm just going to give you the benefit of the doubt here. 

n/a Points
2017-02-28 8:58 pm

I have the same problem you described.  Did you ever find a fix?  TR

n/a Points
2015-05-23 4:54 am



I am Idrees working in a buying office and do communication with my different buyers.

I am using Microsoft Outlook for communication with buyers. I am facing some problem with my email account as i am getting email attachments with winmail.dat.txt instead of regular pdf files. My other coleagues receiving the same email with pdf attachment, while i am getting the email with winmail.dat.txt attachment. 

Please confirm the method how I can resolve this issue. Due to this issue I can't be able to get actual attachments those are my buyer sending in pdf format.




10,077 Points
2015-05-27 12:19 am
Hello Idrees,

Has your buyers followed the steps to prevent outlook from converting the file to a winmail.dat file? Even if you make these changes they would have to as well.

Best Regards,
TJ Edens
n/a Points
2015-03-09 2:45 pm
photo attachment to an outgoing Outlook email received on an Ipad in 'winmail.dat'. The advice in the article does not fix that
n/a Points
2014-12-27 10:35 am
How to send Excel or Word ATTACHMENTS via Outlook and have them arrive as .xls or .doc NOT winmail.dat

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