Open Winmail.dat: How do I open a .DAT file?

Don’t be afraid of viruses if you receive a mail with an attachment in .dat format. This is a completely harmless format (in most cases). We will explain how to open Winmail.dat and what is actually behind it.

Open Winmail.dat

Many different programs use the “.DAT” extension to store various contents. However, the best known is the file “Winmail.dat,” which is sent as an attachment with many emails. The file is often automatically attached to an email if you sent the email with Microsoft’s email program Outlook.

How do I open a .DAT file?

Here we show how to open emails with the Winmail.dat attachment. We also show how to set up the PC to send the emails without the .DAT file: This way, email recipients who do not use Microsoft Outlook can read the emails correctly. So feel free to forward this tip to the email sender!

Besides email attachments in DAT format, another type of this file extension is known and widespread: DAT files containing videos. These need a certain player, often renaming the file extension helps to play them.

The attachment “Winmail.dat,” which is often sent with emails, is more difficult to open: This attachment is automatically sent with Microsoft Outlook emails. However, you can open the file with the following tricks.

What is Winmail.dat?

If you receive an email with an attachment called Winmail.dat, you are a user of a mail client such as Mozilla Thunderbird or something else, and secondly, it is a special format that comes from the fact that the sender of the email has sent it via Outlook. Because Microsoft’s mail client has 3 different formats:

  • Text only
  • HTML
  • Rich-Text

While the first two formats can be opened and read by almost every mail client, Rich-Text or RTF is an in-house format of Microsoft, which usually only Microsoft email programs can open. And this format has the extension .dat.

What does the Winmail.dat contain?

The Winmail.dat contains information about the format of the email. So if you receive the email via Microsoft Outlook, it will be displayed in the format as the sender has set it up.

However, this formatting is mostly missing on other mail clients, and the attachment is sent instead. Also, the Winmail.dat can contain attachments.

So you should always make sure that if you send emails with Outlook, you only use the rich text format if you are sure that your recipients also have a Windows mail client.

Open Winmail.dat under Windows

The Winmail.dat file is automatically created with Microsoft’s email program “Outlook” or the free variant “Outlook Express” and attached to outgoing emails. If you open such an email with Outlook, it automatically recognizes the attachment and displays the email, including the attached files.

Without Outlook, you have to use additional programs like the free “winmail” to view the file’s contents. With “winmail” (for Windows and Linux), you can unzipped the attachment “winmail.dat” can be, and you can extract the originally attached contents again.

There is also the free “Winmail Opener” from EOLSoft, which can also recognize and extract the rich text (RTF) contents of the attached Winmail file. Also, with this, you can view the actual content of the attachment.

Winmail.DAT with the Apple Mac

If you use Mac OS or don’t want to download an extra program under Windows, you can also convert the Winmail.Dat file online on the Swiss website “” The files sent there are supposed to be deleted afterward, but the service is still not intended for top-secret emails.

Or you can read our another detailed article on how to open a Winmail.dat file on Mac.

Open Winmail.DAT on iPhone/iPad

If you get an email on your Android phone or tablet that sends the file “Winmail.dat” instead of the actual attachment, there are special (free!) apps in the official Android Store that can open the file and copy out the actual attachment:

Only with extra software or online

If you want to open the email sent to you with Winmail.dat to see if you would miss attachments; otherwise, you have to use the software. With Winmail Opener, you can open and read the attachments in .dat format. You can download the program from our button:

Simply open the downloaded file with the tool, and you can read the contents.

Open Winmail.dat online

There is also the alternative to open the attachment via the online service However, the data is temporarily stored for processing, which could possibly cause a problem with the data protection regulations.

If you have nothing to hide or you don’t mind that the data may be on the Internet, you can also use this service:

I send emails with Winmail.dat attachment myself – Solution!

If you use Outlook as your email program, you have probably been pointed out to it by other email users: If the email program Outlook is not set correctly, it sends the emails in the wrong format.

If the recipient also uses Outlook, it will not notice this. But if the recipient uses another software, the email and attachment are often not displayed correctly: You cannot open the DAT file attached by Outlook. Users of other email programs are therefore unable to view the sent files.

If you use Outlook 2007 or Outlook 2010, this small “ifixit” tool from Microsoft helps to check the incorrect settings quickly and easily: To do this, the tool “Microsoft Fix it 50041” must be downloaded from this website run. The repair program then corrects the incorrect Outlook settings.

Enjoying this guide on Open Winmail.DAT file? You can also read Open the Winmail.dat on iPhone, iPad and Mac

Adjust Outlook settings

Nevertheless, the Outlook settings must also be checked and possibly adjusted. You can set the format for outgoing emails in the “Write” or “Send” settings. Here you can choose between “Text”, “HTML” and “RichText” (RTF).

While most other email clients can handle text or HTML format, very few email clients can display RTF emails in RichText format: Here, only the Winmail attachment is displayed instead of the actual email.

Attention: You can still save the send settings for each contact separately: If only one recipient complains about unreadable emails or attachments as Winmail.Dat, you can change the settings to “Text” or “HTML” only for this contact.

DAT video files

Another well-known form of .DAT file is MPEG videos in VideoCD format. These MPEG video discs were the predecessor of the DVD, but with much lower resolution. If you copy the video contents of a VideoCD, you will find multiple.DAT files, but the video contents are usually movies in MPEG format.

These can be opened and played with media players such as the free VLC Player. These files must contain the extension .DAT only for video CDs. If you want to save them on your hard drive, you can also rename them to .MPG: This makes it easier to recognize that it is a video file.

Windows automatically adjusts the program icon after renaming. If you cannot open such a MPEG video file in a player, it should be recognized and played at the latest after renaming the file extension from “.DAT” to. “MPG.”

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