What is Winmail.dat File

What is Winmail.dat File

What is Winmail.dat File? How To Prevent Outlook From Sending Winmail.dat File


The Winmail.dat file format is one such format that holds information about the Rich Text message format. However, if you send a mail to someone who doesn’t have this format available then they will receive the message with the Winmail.dat file as an attachment.

This means that the mail is almost negligible and inaccessible to the user. In many cases, renaming Winmail.dat attachment to actual attachment may allow you to recover the attachment.

It could also by using HTML or plain text when you are composing an email. In order to learn how to configure Outlook to stop sending Winmail.dat files, scroll down below.


How To Prevent Outlook From Sending Winmail.dat File?


Method 1: Changing Default Message Format

Here are some steps mentioned below which you need to follow in Outlook clients settings to prevent open Winmail.dat. This method changes the default messaging style and applies to all the emails going out.

Step 1:

Log in to Outlook, click on File and you will reach the Account Information page. Here, click on ‘Options’.
Step 2: As soon as the interface changes, click on Mail from the left-hand side. Now go to the section of ‘Composed messages in this format’ and drop down the menu beside. Choose ‘HTML’.
With this, any mail that you send from Outlook will remove Winmail.dat as an extension and send in the required HTML format.

Step 3:

Once set, we need to go to the Message Format section once again to change the settings. Scroll down on the same interface until you find ‘When sending messages in rich text format to internet recipients’.

See another drop-down here click on it and set it to ‘Convert to HTML format’. Choose OK here when changes and you will be able to save your settings.

Method 2: Disabling Winmail.dat For Individual Clients


To make changes as required, go to the email which you are composing at present in Outlook.

Step 1: Reach to the To: field and right-click on the email address to which you want to send an email.

Step 2: Select ‘Open Outlook Properties’.

Step 3: Look for ‘Internet Format’ and choose ‘Send plain text only.

Step 4: Click OK and your changes will as you were looking for.



If you are not able to use Open Outlook Properties here then we have a workaround available. This particular workaround helps with ‘Let Outlook decide the best sending format’.
For this, open the contact from the contact folder with the double click and remove the email address here. Now save and close it.

Re-open the contact again and retype the email address manually without copying. Also, do not auto-complete the email address as well. Now save and close the contact.


Method 3 Using Rich Text Internally & Not Externally

This method is meant if you prefer using Rich Text message format for internal purposes but avoid using it to send outside. It is possible to send HTML or plain text only to external contacts by tweaking a small setting.

Go to File > Options > Mail > Option group: Message format >option.
Choose the above format when you wish to send Rich Text format or Winmail.dat format.


Method 4 Change On Message By Message Basis

No matter if you have made a default choice already, you can still make the changes in a message format to any other email format whenever required. It is required that you create a new message for this or choose the reply/forward button to go ahead. Once done, follow the instructions mentioned below.


Simplified Ribbon on Microsoft 365: Format Text > Click on the ellipses present (…) on the right > Message Format

Classic Ribbon: Format Text > Option group: Format

Reading pane Reply/Forward: For this, click on the pop-out button presented above the message in order to open the email in your own window.

Done? Now use the above methods to make the changes according to your convenience.



We hope that this blog must have explained to you what this Winmail.dat format is and why it shall be customized when required.

It is understood that not every client has this format present and they need an easy-to-read and available content reading part.

This is why we have explained to you different methods to prevent Winmail.dat so that every user and client, who is receiving email and doesn’t hold Rich Text format can access the required content.

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