stop sending or receiving winmail.dat attachments in Outlook client that is configured incorrectly, the receiver may receive an attachment with the name winmail.dat. This is a binary attachment that includes the formatting information of the email message. In addition to this, the winmail.dat attachment may also include the sender’s personal folder path and log-on name.
Make sure your personal information like your .pst file path and log-in name aren’t included in any winmail.dat attachments by stopping Outlook from sending them. This article will show you how to stop Outlook from sending or receiving winmail.dat attachments.
What is the winmail.dat file?
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Microsoft Outlook and Microsoft Exchange Client can send email messages using Transport Neutral Encapsulation Format (TNEF). This is done when Rich Text Format (RTF) is enabled in Outlook.
The following information may be included in the binary attachment winmail.dat: The binary attachment winmail.dat may include the following information: sender information, recipient information, message body text, and/or attachments.
- The email message’s formatting information, like font style, color, etc.
- The OLE objects, like embedded pictures, can be viewed by using the OLE Viewer.
- Special Outlook features, like voting buttons, custom fonts, etc., make it easier to stay organized and improve productivity.
- Regular file attachments.
The “winmail.dat” attachment may also contain the sender’s info, like the path to their .pst file and log-in name. The recipient can’t read this until they open the “winmail.dat” file with binary or text editor software. The sender’s password is never revealed to the recipient.
The recipient’s email client will determine how they see the email encoded in TNEF – whether or not they’ll be able to see features like voting buttons will depend on if their email client can decode TNEF.
How to stop sending or receiving winmail.dat attachments on Outlook
One of the following two things will happen if the email client of the receiver does not support TNEF encoding and decoding or does not understand the TNEF format:
- He will get an email with the attachment called winmail.dat in plain text format.
- He will get the email in plain text format, with an attachment with a generic name like nnnn.dat or nnnn.eml, where nnnn is any random number.
It is important to stop Outlook from sending winmail.dat attachments. You can try the following methods to see which one works for you.
- Change the Compose messages setting in Outlook
- Type the email address of the recipient manually
- Delete the recipient’s contact and create it again
- Disable TNEF in Windows Registry
- Disable Rich-text format on domain
1] Change the Compose messages setting in Outlook
The recipient will receive the winmail.dat attachment if the Compose messages setting in Outlook is set to RTF (Rich-text Format). To stop Outlook from sending the winmail.dat attachment to the recipients, change the Compose messages setting in Outlook.
- Open Microsoft Outlook.
- To change your Outlook options, go to “File > Options.” This will open the Outlook Options window, where you can change various settings.
- From the left side, select the Mail category.
- To compose messages in HTML or Plain Text format, click the Compose messages in this format drop-down and select the desired format. This option can be found under the Compose Messages section.
- Scroll down to the Message format section.
- Convert to HTML format or Convert to Plain Text format when sending messages to Internet recipients.
- Click OK to save the settings.
After performing the above steps, Outlook will send all the email messages in the format you selected. Hence, the recipient will not receive the winmail.dat file attachment in the email message. You can choose the HTML or Plain text format for a particular recipient just before sending the email message. To do this, follow these steps:
- Open Microsoft Outlook.
- Click New Email under the Home tab to open the Compose email window.
- Click on the Format Text tab.
- Under the Format group, select the HTML or Plain Text option.
2] Type the email address of the recipient manually
If you’re having trouble sending email to someone using the Address Book, try typing their address in manually instead of selecting it from the Address Book. This trick has helped many users.
3] Delete the recipient’s contact and create it again
If the above method did not help you fix the problem, delete the recipient’s contact from Outlook and add it again. To delete a contact in Outlook, follow these steps:
- Open Microsoft Outlook.
- Click on the People icon on the navigation pane. You will find it on the bottom left side.
- delete the contact you want by clicking the Delete button.
4] Disable TNEF in Windows Registry
If you’re still seeing winmail.dat attachments in Outlook, you can disable them by editing your Windows Registry. Be careful when editing your Registry keys, as any mistakes can cause serious problems on your system. We recommend creating a system restore point before proceeding.
Launch the Run command by pressing the Win + R keys. In the Run command box, type regedit and click OK. Click Yes in the UAC prompt. When the Registry Editor opens, copy the following path and paste it into the address bar. Hit Enter.
Check if the “Preferences” key is selected from the left side. Then, check if a “Value” named “DisableTNEF” exists on the right side. If not, you have to create it. To do this, right-click on the empty space on the right side and go to “New > DWORD (32-bit) Value.” Right-click on the newly created value and select “Rename.” Name it “DisableTNEF.” The “Value Data” of all newly created values is 0 by default. You have to change it to 1. To do this, right-click on the “DisableTNEF Value” and select “Modify.” Now, enter “1” in the “Value Data” field.
5] Disable Rich-text format on domain
You can disable the Rich-text format on Domain to stop Outlook from sending winmail.dat attachments to the recipients by opening the Exchange admin center and going to “Mil flow > Remote domain.” Now, double-click on your domain and select Never in the Use Rich-text format.
You may need to ask the sender to adjust their Outlook compose message settings if you’re only receiving winmail.dat attachments. This will ensure you receive all future emails in either plain text or HTML format.
How do I stop receiving winmail DAT files?
Currently, there is no option in Outlook to stop receiving winmail DAT files. To stop receiving these attachments, contact the sender and ask them to change their Outlook Compose messages settings from Rich-text format to either HTML format or Plain Text format.
How do I stop Outlook 365 from sending attachments as winmail dat?
To prevent Outlook 365 from sending attachments as winmail dat, you will need to change the Exchange settings. Open the Exchange admin center, go to “Mail > flow > Remote domain.” In the Rich-text format section, select “Never.”
Hello, My name is Shari & I am a writer for the ‘Outlook AppIns’ blog. I’m a CSIT graduate & I’ve been working in the IT industry for 3 years.