Home Tech What is Winmail.dat file & Open Winmail.dat file

What is Winmail.dat file & Open Winmail.dat file



What is Winmail.dat File Format – A Complete Guide

What is Winmail.dat File?

A winmail.dat file is created by Microsoft Outlook and Microsoft Exchange server. It can be a rich text formatting for emails. It also can be an actual email attachment file which is wrongly identified with winmail.dat file extension but it is actually an Excel spreadsheet, a word document, calendar invite, RTF file or some other type of file that is attached to the email message. This file is also known as Transport Neutral Encapsulation Format or T.N.E.F file.

TNEF is a technical term which is used for Outlook users. If TNEF or Winmail.dat file format Error exists in outlook emails, then different methods can help to view and open winmail.dat file. This article gives you a brief information about what is Winmail.dat file format and how to prevent receiving it in email applications.

When And How Winmail.dat File Is Created

After knowing that what is Winmail.dat file, you can explore below how this T.N.E.F file created. A winmail.dat file occurs because the various email programs handle the message in different file formats. When MS Outlook user sends an email message in rich text format instead of plain text format then a winmail.dat has created. Mac users typically find a winmail.dat format file in emails sent from the Windows-based system and Mac mail not able to open and read winmail.dat file in the mail application.

User’s Queries Related To Winmail.dat File Extension

Query 1: I have received an email from Outlook attached with winmail.dat file extension. I do not know anything about what is winmail.dat file format and I have no idea that how can I open winmail.dat extension file. Is there anyone who can help me to view winmail.dat file information? Please share your views.

Query 2: I used Mac OS X based machine and I have winmail.dat attachments in my email. I want to know about that files and I also want to know that how can I prevent receiving of that winmail.dat extension file. Please provide me the solutions.

Query 3: Is there any way to view Winmail.dat Attachment Files on Mac OS X?

How To Prevent MS Outlook From Attaching Winmail.dat Attachments

There are two methods available to prevent sending of the winmail.dat attachments within emails. These solutions are described as below:

Solution 1: Change The Default Setting Of MS Outlook
There are different ways to change the default message format in different versions of Outlook. Follow the below-mentioned steps as according to your MS Outlook version.

In Outlook 2007 and older versions

  • Open MS Outlook and then go to Tools > Options > Email Format > Internet Option.
  • Then choose Plain Text from the drop-down menu under compose messages.
  • After that, Click OK button.

In Outlook 2010 And Earlier Versions

  • Open Microsoft Outlook and then Select File Options Mail.
  • Then select Plain Text from the drop-down list under compose messages.
  • After that, Click on OK button.

Solution 2: Create Recipients list in PAB(Personal Address Book)

Follow the below-mentioned steps to create a recipient list in the personal address book:

  • Open MS Outlook and then Click on Tools > Address Book > Personal Address Book.
  • Select the addresses which you want to sent as Plain text and then choose File Properties.
  • After that, unchecked “Always send to this recipient in Microsoft Exchange rich text format” box in SMTP General tab and then Click on OK button

How To Open Winmail.dat File On Mac OS X

There are two possible ways to view the winmail.dat file on Mac OS X. Here, we are going describe these two methods in details.

Method 1: Save the Winmail.dat File As The Intended File Type

Go through the below mentioned to steps to save and read the winmail.dat file as intended file type:

  • Open the email that contains winmail.dat file.
  • Right-click on the mail that has winmail.dat file and then Click on Save Attachment.
  • In the Save As dialog box, replace the ‘dat’ extension with the intended file type like .docx, .pdf and then Click on Save button.

After that, you can open winmail.dat file without any problem in Mac OS X.

Method 2: Forward The Emails having Winmail.dat File To Gmail

To view winmail.dat file attachments data, a user can forward the emails consists winmail.dat file to your Gmail account. Since Gmail is a web-based email application and it can handle winmail.dat file format without any difficulty. It always accurately read winmail.dat file as either an accurate file attachment or a rich text formatted email. Therefore, forwarding those emails which have winmail.dat files to Gmail is one of the solutions to open winmail.dat file.

How To Stop Receiving Winmail.dat Attachments Again

If a user is receiving winmail.dat attachments and he does not want to receive winmail.dat files then he has to turn off TNEF in their MS Outlook application. This method is useful when users no longer want to view winmail.dat file and want to disable receiving of email messages having winmail.dat attachments again.


This article is an effort to describe What is Winmail.dat file, a winmail.dat file format usually appears due to various email applications, which handle messages in a different format. This file generally comes with Outlook emails because MS Outlook is not able to read winmail.dat file have information with the rich text format. By changing the default message format in Outlook, users can prevent sending of the winmail.dat attachments with Outlook emails. Users can also stop receiving winmail.dat files by turn TNEF off in Microsoft Outlook application. To view Winmail.dat file in Mac OS X, a user can follow the methods mentioned in above information.