How to change the mailing format (winmail.dat) in Outlook

Although it is not a common occurrence, in many cases, we receive attachments with the winmail.dat extension in our email accounts and can be alerted because we do not know for sure what type of files they are. Let’s see how you change the mailing format in Outlook.

Winmail.dat is a file type that contains information about messages that use Microsoft’s proprietary TNEF format. For this reason, these message types are not recognized by other email clients.

Change the mailing format.

Change the default format for sending messages to plain text.

This is where the message sender changes the format of all emails sent in plain text:

For version Outlook 2016, 2010

  • Click File
  • Select
  • Click on Mail Option
  • Within the message format, in the option “When sending messages in rich text format to internet recipients:” we select Convert to plain text here.
  • We accept, and that’s it. This way, it will always be compatible with all recipients sending messages with attachments.

For Outlook version 2003, 2007

  • Click on Tools.
  • Click Mail format.
  • Click Internet Format.
  • In the Outlook Rich Text options, click Convert to HTML Format or Convert to Plain Text (the latter option is the best option to ensure that attachments reach all recipients).

Suppose you want certain recipients sent in RTF rich text format and others in plain text format. In that case, you can do that by going to the Contacts area (Address Book) and setting everyone the type of sending format you consider appropriate. It is the next option.

Change sending format to contacts in the address book

We have seen the different options to know the content of Winmail.dat in Windows and macOS environments.

The sender can use the following steps to remove the RTF format from certain recipients who say that the attachments you send cannot open it (and you don’t want to set the above option for all recipients). You enter the address book (contacts).

For Outlook 2010 version

We go to the Outlook address book (Contacts).

We go to the contact and press the right button (in which we want to change its format when sending things).

  • Click on the contact card
  • Click on the settings icon and then on Outlook properties (see the picture)

As you can see in the figure below, you can choose what format it should have when you send emails to this specific contact. If you select the “Send plain text only” option, this contact will no longer receive the famous winmail.dat attachments. We accept, and that’s it.

For Outlook 2016 version.

In Outlook 2013 and 2016, this option is disabled by default, but we can see the options by making a slight change in the registry.

Go to the following path depending on the Outlook version:

Outlook 2013

HKEY_CURRENT_USER \ Software \ Microsoft \ Office \ 15.0 \ Common \ Contactcard

Outlook 2016

HKEY_CURRENT_USER \ Software \ Microsoft \ Office \ 16.0 \ Common \ Contactcard

Now, regardless of version, right click with the new named key turnonlegacygaldialog, enter REG_DWORD and the value 1.

Note: For some reason, the last path of the contact card is not shown. We will leave you the manual registry file for each version, which will add all files directly to the registry when run. After execution, you will have the option in Outlook.

If we return to our Outlook and open the Contacts tab, we see that the same feature as in Outlook 2010 is already displayed. Click on Open Outlook Properties.

In the new window, we can edit the Internet sending format of this contact.

With these solutions, you can change and fix the winmail.dat file format error that occurs on both Mac and Windows 10 systems.

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