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Convert TNEF to MSG

Convert TNEF to MSG
Decode Winmail.dat, ATT00001.dat and other TNEF attachments to Outlook MSG format. After that you can open and view it with Outlook.
Version: 4.21 released on May 11, 2023.
Tags: msg convert
(4.7 / 57 reviews)

Convert TNEF to MSG for Outlook
You can download a free limited version down below

Main features

  • Converts winmail.dat, ATT00001.dat, and other TNEF attachments.
  • Decodes TNEF files of all Outlook versions.
  • Converts winmail and other TNEF DAT files with all data: message properties, formatting, images, hyperlinks, and attachments.
  • Has no size limitation of the TNEF DAT attachment files.
  • Allows renaming source winmail.dat files.
  • Compatible with all Microsoft Windows versions.
  • Creates a log report after each run.
  • Extremely easy to use.

What are winmail.dat and TNEF files

What are DAT files

The .dat file extension is common for files that may contain any type of data: text, images, videos, or configuration. The specifics of this extension are that the information in these files is intended for the software, not for the user. Usually, .dat files contain plain text or binary data. The main purpose of DAT files is to store program settings and properties.

What is the TNEF format

TNEF (Transport Neutral Encapsulation Format) is an internal Microsoft Outlook format. It is used for data encapsulation (transmission). If the destination email client does not support the TNEF format, then the message will not be displayed properly.

In case of receiving such an encoded TNEF message, the recipient will see a regular text message with an attachment, usually named Winmail.dat or Win.dat.

What are att00001.dat, att00001.eml, winmail.dat or win.dat file types

The original version of the message in TNEF format is packaged as an attachment to the received message with plain text. Most often this attachment has the name Winmail.dat, Win.dat or another common name, such as AttNNNNN.dat or AttNNNNN.eml, in which the NNNNN is a random number: 00001, 00002 etc.

These DAT attachments may contain the following information:

  • the original formatting, like fonts, text sizes and colors;
  • OLE objects (for example, embedded images or Office documents);
  • special Outlook elements: custom forms, voting buttons, Outlook calendar data, etc.;
  • internal message properties used to work in Outlook;
  • attachment files from the original message.

How to open winmail.dat TNEF file

Since TNEF files, which contain winmail.dat attachments, are created by Microsoft Outlook and Exchange Server, to open them, you need to install one of the apps that support TNEF format: Microsoft Outlook, Office 365, Outlook Web Access, Microsoft Outlook Express.

However, even if you use one of these programs, you still won't be able to open winmail.dat attachments in TNEF messages, or previously saved winmail. And despite using Outlook, you can continue to receive emails with non-clickable winmail attachments.

You can have two variations of TNEF files:

  1. A message with TNEF attachments, winmail, windat, att00001, for example, in EML format.
    Here, to open files with winmail.dat attachments, you can simply convert them from EML to MSG format with the EML2MSG converter. This program automatically decodes .dat attachments in message files. If you've got Inbox emails with winmail.dat attachments in your mail client, first export them to EML using the Outlook utility or another mail client's suggested solution. After that, import the resulting files into Outlook using a special add-in for importing EMLs.
  2. A saved attachment with a .dat extension.
    The easiest way to view such winmail.dat, win.dat or att00001.dat files in Outlook is to convert them to MSG.

Why winmail.dat to MSG conversion?

Outlook users may need to convert winmail TNEF to MSG due to some reasons.

Quick access to winmail / att00001 .dat attachments

The recipients with the accounts on Microsoft Exchange Server also face the problem of receiving emails in TNEF format with non-opening winmail.dat or att00001.dat attachments. These can be messages from important people, for example, management or a valued customer. In such a case you need a simple tool to open those DAT attachments quickly, without the need to call an IT specialist. After TNEF2MSG conversion the DAT files can be imported into your mailbox as ordinary messages and be accessible when needed.

Export archived winmail.dat files

If you use Outlook and have archived TNEF files, you will most likely prefer to store them in MSG format. This is the most convenient file format for Outlook archives, as you can open MSG by double-clicking at any time and in any Outlook version.

Forwarding TNEF messages

If you sometimes receive TNEF messages with winmail.dat or similar DAT attachments, then you may need to quickly forward them to clients, partners, or colleagues. Here, you cannot send them onward in an unreadable form and without a preview. You must first transform them into a readable format before sending them on. By quickly converting winmail to MSG, you may continue the communication.

Online conversion hazard

Many services offer online winmail.dat conversion. With the simplicity of this method, you need to remember its risks and disadvantages.

First, it is the safety of information. By transferring any information to a third party's website, you risk it becoming widely available. This is especially unsafe with DAT attachments, the contents of which you may not guess, and it can be whatever data.

Another disadvantage is that transferring and downloading data online requires a stable Internet connection. With bulk file download, it takes time, attention, and sometimes extra funds.

How to import winmail.dat files to Outlook

To import winmail.dat or att00001.dat or other TNEF attachment file to Outlook, follow few simple steps with the "Convert winmail.dat TNEF to MSG" tool:

  1. Launch the "Convert winmail.dat TNEF to MSG" utility from Outlook Ribbon or standalone app.
  2. Browse for saved winmail.dat or other TNEF attachment file on your computer.
  3. Specify the destination path and the name of the resulting MSG file.
  4. Mark to overwrite existing files if there are files with the same name in the destination folder.
  5. Run the winmail.dat TNEF converter.

After converting to MSG, you can import winmail.dat in Outlook. Just drop it down into the desired Outlook folder. You can also open the file by double-clicking it.

Batch winmail TNEF conversion

The utility provides possibilities for bulk conversion of winmail.dat files helped by batch scripts. To do this, use a separate console application in the product. Click on the command line option button and you will see the ready-made settings to run at the command line. You can also contact our technical support for help to create your script.

Convert winmail TNEF files on a schedule

To convert winmail and windat to MSG format periodically and regularly, use the command line utility and Windows Task Scheduler. With them you can flexibly set up a schedule for automatic windat conversion from the desired account without logging in manually.


If you receive an email with an attachment called winmail.dat, win.dat, or ATT00001.dat, it is most likely a message from an Outlook user with a specific configuration of his mailbox. Because of this configuration, messages are sent in a special TNEF format.

If your email client or your Outlook settings differ from those of the sender, you cannot read winmail.dat TNEF attachments. You can ask the sender to change their settings, but this is not always possible. Sometimes, you can view a text part of the email in the message body, but you can't see the original message subject, images, and email attachments.

So, what if you need to quickly proceed with this message and get access to all the data inside winmail? To deal with it in Outlook, use the "Convert winmail.dat TNEF to MSG" add-in. This winmail.dat converter migrates all original message data and metadata to the resulting MSG files. Open the cryptic winmail.dat in the familiar interface and import the initial email in your mailbox in a few minutes.


What is the difference between winmail.dat and TNEF files?

TNEF is the name of the Outlook data encoding. When working correctly, Outlook decodes data from this format to display the message correctly. If the recipient, for various reasons, receives an encoded TNEF message, it looks like a text message with a winmail.dat attachment file. This winmail.dat attachment contains the original TNEF encoded message, and the text of the received email represents the unformatted text of the source message.

Why do I receive winmail dat attachments?

If the sender uses RTF (Rich Text Format) for creating messages and the recipient's mail client does not support this format, the original message comes as a winmail dat attachment.

Can a windat file be dangerous?

Unlike most other DAT files, the origin of winmail.dat and win.dat files is clear. However, since they are attachment files, you should not auto open them. Use an antivirus program to scan all the received mail and only open email attachments from people you know.

How do I open a winmail attachment with windat converter?

Once converted to MSG, a TNEF winmail attachment can be opened in Outlook. Just double-click the resulting file and you will see the original message with the source formatting and all the additional information.

Do I extract the email attachments using this winmail dat converter?

Yes, the utility creates a new .msg file with all the data from the source email, including attachments.

Can I use this winmail.dat reader on my Mac?

No, this software is designed for Windows PC. You need a MAC application to view TNEF files on MAC

Can I convert multiple winmail dat files at once?

With the command line app, you can convert an unlimited number of winmail files from different locations simultaneously.

OutlookFreeware.com Outlook Ribbon
All utilities easily integrate with Outlook (optionally)

* This utility is for non-commercial home use only. It will not run in domain enviroment. Some of the described features and support for domain enviroment are available in advanced version of the utility only. Free version may have additional limitations.

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