Repair DAT file & Resolve Winmail.dat – ATT0001.dat file Error
This article describes manual methods to repair DAT file errors faces by the users. It also includes solution to repair Winmail.dat file or ATT0001.dat file error. This will provide a manual solution to resolve and recover DAT file error easily to solve user query.
What is a DAT file?
The DAT extension stands for Data file. A Data file is used by the different application to store generic information pertaining to associated application. Various application creates DAT file extension to store data related to applications. A DAT file does not store the main information such as code, program files and data structure file but store only the input & output file information used by any another program.

A DAT file store data file in two files:
- Text file
- Binary file
A Text file hold information in ASCII Characters form. You can see Text file content by opening file in Text editors such as notepad or Notepad++.
A Binary file holds the data information in binary format ( 0 or 1). These files are easily read and written by other program as compared to Text file. Since Text file includes some special character marking the termination of a text line (called End Of Line) & it takes time during internal translation.
Whenever the text or binary file gets corrupted, it resuls in formation of DAT file extension within email attachments. To resolve DAT file extension error, You can look manual methods mentioned below to fix repair dat file.
About TNEF file
TNEF acronym stands for Transport Neutral Encapsulation Format (TNEF). It is a technical term used for a special method to pack information while sending a message via internet between the applications. Many application uses TNEF Encoding in email clients for sending image, and videos.
A TNEF message contains a plain text or binary format file to hold information corresponding to the original message.
Binary text file attached to the original message includes information such as:
- Font, styles, and colours information.
- OLE (objects linking and Embedding) objects embedded pictures and embedded Microsoft Office documents.
- Special Outlook features (custom forms, voting buttons).
How to Identify TNEF file?
You can identify a TNEF format with the help of its extension. All attachments with name "Winmail.dat" belong to TNEF file. If an attachments have .dat or .eml extension then this file belong to non-TNEF attachments.
Sometimes is also referred
as Part 1.2 file (when there is anti-virus installed in the system). A Winmail.dat created within emails attachments of Outlook are referred to TNEF.
Winmail.dat file Error
Winmail.dat files are also known as TNEF file. A Winmail.dat file created in many email clients application based on different file format. Some Outlook features require TNEF encoding which is correctly understand by another Outlook user across the network to display the emails.
Cause for Winmail.dat File formation
A Winmail.dat file is created due to an error in configuration setting or message format. For instance, whenever an Outlook users sends attachment within message having rich text message format to another user with diverse email client, & other user has configured its account to receive emails with the normal plain text format. The Receiver Email-client will not be able to open the emails and a Winmail.dat file created within email. To fix DAT file cause, a user can apply different methods to recover DAT file as mentioned in this blog.
How to Repair DAT file Error
To repair Winmail.dat files in attachments, you can use the manual method to recover DAT file attachments. These methods can easily fix DAT file issues.
Manual Method to Repair Winmail.dat file Error
Manual method differ according to different email client configuration and platform setting to repair DAT file issues. These are manual methods to repair DAT file, you can use given methods to recover DAT file issues.
Method 1: Change the default message format in Outlook
A sender can change the message format of the email before sending messages by following steps:
- Go to Tools >> Click on Options >> Select Mail Format.
- In Compose in this message format list >> Select Plain Text and then click OK.
Note: If certain recipients use an RTF format to receive a message with attachments, then you have to create another Personal address book from them.
Method 2: Create Recipients list in Personal Address Book
A user can select an address in PAB (Personal Address Book) and select plain text format for those addresses. Follow the steps to create new recipient's list in Outlook:
- Go to Tools >> Click Address Book.
- In Show Names From >> Click Personal Address Book.
- Select the addresses that you want to set as plain text >> Click Properties on the file menu.
- In SMTP General tab >> Uncheck the box Always send to this recipient in Microsoft Exchange rich text format.
- Click OK.
Now after changing setting in address book for specific user, all files send in form of plain text using exchange server. Receiver don’t have to recover DAT file from the attachments.
Method 3: Change the Specific Contact Format
To set plain text in recipient's contact record follow the following steps:
- Open recipient's record in the Contacts folder.
- Double-click on recipient's e-mail address.
- Click E-Mail Properties dialogue box >> Click Send Plain Text only below Internet Format.
Method 4: Configure Outlook Rich Text Format Email Setting
In Outlook 2003 and Outlook 2007, you can recover Winmail.dat file by following below steps:
- Click Options >> Tools menu >> Mail Format tab.
- Click Internet Format.
- Select from the list of Outlook Rich Text Format options, click either "Convert to HTML format " or "Convert to Plain Text format".
Using all above-mentioned method and changes in message format in user account settings. A user can easily repair DAT file error in Outlook and other email clients.
ATT001.dat file
An ATT001.dat file is a plain text file, created when a client is unable to identify the TNEF part of the message, Since it also unable to recognize the Winmail.dat file name, so it creates a file name to hold the TNEF information in Recipients emails along with attachments called ATT0001.dat file.
Cause of Corrupted ATT0001.dat file
When a user adds text after the attachments in emails through Microsoft exchange server. Exchange Server always insist that message text should always first and attachments should be in last in emails.
When an email consists attachments first and read by Microsoft Exchange Server, then exchange server stops looking for text and treat anything else as attachments. Any remaining text section now converted into attachments with a fake name called ATT0001.dat file. You can recover ATT0001.dat file by using manual method.
Manual method to Repair ATT0001.dat file
Manual Method simply fix Dat file error in emails. Always try to use text sections before attaching any attachments for preventing this issues. If you follow the correct method of sending messages with attachments and signatures, chances of getting error ATT0001.dat file become low. If user not able to repair DAT file error then user can go for alternative solution to recover DAT file information.
Alternative Solution To Fix DAT file
You can go for free as well as paid solutions to repair DAT file. Download DAT file from the email and use online tools to extract data from it. Otherwise, a Third party recovery tools are also available to repair DAT file.
Note: Email client (Thunderbird) uses Lookout add-on to recover ATT0001.dat file. Lookout in Thunderbird encoded attachment in TNEF to recover DAT file information.
Conclusion
This article describes manual solution to recover DAT file effectively without any problem. It also describes how DAT File is used to store generic information related to the application, DAT type: Text and Binary files, Winmail.dat and ATT0001.dat file error that are related to DAT file.
You can solve any Winmail.dat file error that occur due to compatibility issues of messages formats between same or different email clients & ATT0001.dat error related to text file error of DAT file. To Recover DAT file, you can use various methods mentioned above to repair DAT file in Email Client(Outlook) or you can fix dat file issue by other alternative solution.