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.

5 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

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