How to Fix Winmail.dat Attachments in Outlook

How to fix winmail.dat attachments in Outlook

Is your Outlook creating winmail.dat attachments with every email you send? Believe it or not, this is a very common problem and here’s how to fix it!

To stop Outlook from sending winmail.dat attachments, set your new emails to compose in HTML or Plain Text format. Also, when sending Rich Text emails to internet recipients, make sure they are converted to HTML format or Plain Text format.

If you aren’t sure how to do that, follow our instructions below.

Why does Outlook send winmail.dat attachments?

When composing an email in Outlook, there are 3 ways to format your email: Plain Text, Rich Text, or HTML. By default, Outlook uses HTML format when composing new emails.

The winmail.dat attachment is added to Outlook when you send an email using the Rich Text format that has text enhancements such as bolding, italics, font sizes or any other features that are available with Rich Text format. The file is attached to the email because it contains instructions on how other email clients should format the text.

This only happens when composing in Rich Text format because Plain Text format doesn’t have the ability to add text enhancements, and HTML format includes all the enhancements in the HTML code itself, so there is no need for a winmail.dat file.

The winmail.dat problem happens with all versions of Outlook from 2003 onwards.

How to Prevent Winmail.Dat Attachments from Being Sent in Outlook

Step 1

Open Outlook, click on File > Options.

Outlook 2016 1

Step 2

Click on Mail from the left menu.

Under the Compose messages section, change the “Compose messages in this format” dropdown box to HTML or Plain Text.

Outlook Compose Message Format

Step 3

Scroll down until you see the Message format section.

In the “When sending messages in Rich Text format to Internet recipients”, ensure you select either Convert to HTML format, or Convert to Plain Text format.

Click OK to close the Options window.

Outlook Convert Outgoing Message to HTML

Preventing Winmail.Dat Attachments in Outlook 2003 – 2007

Step 1

Open Outlook, click on Tools > Options.

outlook 2007 1

Step 2

Click on the Mail Format tab at the top.

Outlook Mail Format

Step 3

Under Message format, change the “Compose in this message format” dropdown box to HTML or Plain Text.

Click OK to close the Options window.

Outlook Message Format

Using the Windows Registry to Stop Winmail.Dat Attachments from Being Sent

Warning: Editing your Windows registry incorrectly or making a mistake can cause irreversible damage to your operating system. It’s not advisable to edit your registry manually unless you absolutely have to. Only use this method if the above instructions don’t work and you’re comfortable editing the registry.

Step 1

Ensure all applications on your computer are closed, including Outlook.

Right click on the Windows logo in the bottom left corner, click Run.

Alternatively, press the Windows key + R to open the Run box.

Windows Run

Step 2

In the text box, type “regedit” and press Enter, or click OK.

Windows Run Box

Step 3

Navigate to the following path:

HKEY_CURRENT_USER\Software\Microsoft\Office\<office version number>\Outlook\Preferences

The <office version number> corresponds to the following versions of Microsoft Office:

Outlook 2019/2016 – 16.0

Outlook 2013 – 15.0

Outlook 2010 – 14.0

Outlook 2007 – 12.0

Step 4

Right click on Preferences, then select New > DWORD (32-bit) Value.

Regedit New DWORD 32-Bit

Step 5

The name for the new registry key should be “DisableTNEF”. Once you have added the name, hit Enter to apply the changes.

Regedit DisableTNEF Key

Step 6

Right click on the new DisableTNEF registry key and click Modify.

Regedit Modify Key

Step 7

Set the Base to Hexadecimal.

Set the Value data to 1.

Click OK.

Close the Registry Editor window, and you’re done! Outlook should no longer be sending winmail.dat attachments.

Regedit Modify DWORD Hexadecimal Value

If you’re still experiencing winmail.dat problems…

If you’ve completed the above steps and you’re still experiencing winmail.dat problems, you’ll need to remove the autocomplete entry for all of your recipients. Autocomplete is when you start typing an email address in a new message, and their email address comes up as a suggestion.

The sending format is saved for every contact in your autocomplete list. So, even after you’ve changed the sending preferences using the above instructions, some recipients that you’ve previously sent emails to may still get the winmail.dat attachment if you dont clear the autocomplete list.

37 Replies to “How to Fix Winmail.dat Attachments in Outlook”

  1. Hi, It’s my works email that uses outlook and attaches the Win.dat files. However, having followed the above instructions, I noted that I am not set up for Rich Text, but still get those attachements and cannot open proper attachments.

  2. Thank you Gordan for a clear and concise fix! I had actually had this problem once before and followed someone else’s instructions on how to fix. Then the problem came back! The missing piece was the removal of the address from the auto-complete. BTW it was great to hear an Aussie accent on a how-to video. Cheers

  3. Awesome! My outlook setting were all correct, HTML, but I continued to send winmail.dat instead of pdf files. This is the first site that has given a registry fix. It works. Outlook is now a useful email client again. Thank you.

  4. Hi there, In July this year I upgraded my work laptop (HP Windows 10) and also installed Office Outlook 2019. Some of my customers (i suspect with older pcs) are experiencing not receiving the pdf of an invoice I send them, only the winmail.dat file. I have done everything you have described here, the HTML settings, tried Plain text, did the regedit, cleared the auto complete, rebooted, but the same problem persists with some of my customers. Can you please offer any more advice on this issue. Many Thanks

  5. Hi Gordan,

    I have been trying to solve this winmail.dat issue for quite sometime. Eventhough I did not exactly understand what was changed by adding Disable TNEF in the registry, it worked !

    Thanks a ton man !


  6. If, like me, you use Thunderbird and are receiving attachments in a winmail.dat file but cannot read them you could try:
    – Forwarding the email to a gmail account and then forwarding it back to yourself. This seemed to work for me.

  7. Thanks that worked a teat. Quick, easy and worked first time!
    All my settings were right for the first part and adjusting the registry did the trick.
    This has been bugging me for way too long so thanks again!

  8. My problem is not with sending winmail.dat files, but with receiving them. I can receive pdf files from third parties with no problem. However, the emails I get from one office go out from them as pdf files but come in to me as winmail.dat files. if I forward those files out, they are received as pdf files by the new recipient. How do I find out if it is me, or the original sender? thanks.

  9. That last bit about autocomplete worked. Could you explain it more clearly please? I don’t understand what the autocomplete does.

    1. Hi Bowi,

      The autocomplete list in Outlook is just a list of email addresses that you’ve sent emails to before. So, when you go to create a new email and you start typing the address in, Outlook tries to predict which email address you’re trying to send emails to in order to make it easier for you so you don’t have to type the whole email address in. It’s the dropdown box that pops up with suggestions when you start typing an email address in a new email.

  10. I am having an issue recently emailing pdf attachments to my govt client. I have 3 Recipients and 13 people copied. My client keeps receiving Winmail.dat files from me. I then email only 1 person the attachments and they are received. My outlook is set to send as HTML. Please help!

  11. Gordan! Can you help? When I clear all the autocomplete list I still get the mail suggestions coming up. Does this mean the autocomplete list has not cleared? Or is the list generated somewhere else and the old info has been cleared?

    Moreover I dont get the delete X when I wish to delete a single suggestion

    1. Hi Laurence,

      If you’re still getting the email address suggestions, even after clearing the autocomplete list, I would say that the clearing hasn’t worked correctly. It’s a bit strange you don’t even get the cross to delete a single address. That seems like it could be something to do with group policy, or a permissions issue with Outlook directly. If you’re on a corporate network, it would likely be a group policy setting perhaps.

  12. It Worked for me, especially the last step of the autocomplete, it saved the day 😀 Great Article

  13. it Worked for me, especially the last step of the autocomplete. I delete account from contact list, its working. Thanks for your article.. very very thanks you..

  14. Thank you for this article, Gordon. It helped me solve the plain text and winmail.dat issue I’ve been having with my work account! I was going nuts trying to figure out why!

    I went through the settings on my desktop, notebook all my mobile devices and even got a support tech from my hosting service to troubleshoot with me. Having eliminated all as possible issues, we finally figured the problem must originate from Outlook somehow.

    The solution was in the last part of your article. It FIXED the problem.

    Thanks again!!

  15. Hi
    Thank you so much for your help! After unsuccessfully going through the internet looking for solutions and contacting Microsoft support, I finally found your site and your solution. The last bit where we have to delete the list worked. Nobody else offered that solution but you. Thank you, you made my day!

  16. Thank You! Thank YOU! This has been a bane for me for some time & you helped me solve it. The final key step that solved it for me was to “Delete the Auto-Complete entry for the “[To:] entry in the sender’s Outlook”. Such an annoying Microsoft Outlook issue with some unexpected possible causes.

  17. I have been trying to fix this problem for years and tried several fixes outlined on several websites. Eliminating the auto complete email name list is the ONLY solution that has worked. THANK YOU SO MUCH!

    1. Hi Prayut,

      If Outlook is displaying the winmail.dat attachment when the email is received, that means the email was sent using Rich Text format instead of HTML. This can only be fixed by the person sending the email, not the recipient.

  18. Great job on solving this issue. Frustrating for the Outlook/Apple collaboration but at least you provided a solution.

    Thank you!

  19. Thank you Gordan for a clear and concise fix! Absolutely rapt that l finally found someone who provided a simple to follow process. It was great to hear an Aussie accent on a how-to video. You ripper. thank you so much …….. Cheers

  20. I have an issue when receiving an email from one bank I get the attachment (xxxxx.dat) I use office 2019, any solution?

  21. Thank you Gordon,
    I have been swimming through forums for some time and your explanation was the most elaborate while being clear and concise. You finally helped me fixed my issue. Much appreciated.

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