Windows File Extension Help Article

April 20, 2018

Last Reviewed: March 22, 2018 - Revision: 4.0

How to Open and View Winmail.dat Files

What prevents your PC from opening WINMAIL.DAT files?
This article explains how to diagnose and fix common errors related to opening Winmail.dat files. Follow the complete set of instructions and apply the recommended software tool to open and view Winmail.dat files.

Recommended Solution: PC TuneUp Maestro (with Open File Support)

PC Tuneup Maestro helps you to identify and repair common problems that prevent your computer from opening Winmail.dat files.

Download Official Driver Update Tool Download PC TuneUp Maestro to enable your PC to open DAT Files
  Click here to start a secure download of PC Tuneup Maestro
Application Name:
PC TuneUp Maestro (with Open File Support)
Developed by:
Microsoft Certified Partner: CompuClever Systems Inc.
Editor's rating:
5 Start Editor Rating (5 / 5)
Software Categories:
Windows file extension repair; Open file support; PC optimization
File size:
2.04 MB ( less than 30 sec. on DSL/ADSL/Cable Modem)
Operating Systems:
Windows 7 (incl. 64-bit), Windows Vista, Windows XP
Free download, scan & analysis; licensed version available
Last updated:
March 28, 2018

Download instruction: Click the Download PC TuneUp Maestro link. Then, click Run in the File Download dialog box and follow the steps provided the installation wizard.

Common Cause #1: Host Application for WINMAIL.DAT Files wasn't Installed Properly.

The most common cause is that your PC doesn't have the right software application installed to read and parse WINMAIL.DAT files. A file extension is the text after the dot of a file name such as: “DAT”.  This suffix portion of the file name is provided by a program or function to distinguish the particular format of the file.  Your computer can differentiate one file format, like “.WINMAIL.DAT”, from other file formats like “.docx” for Word documents or “.xlsx” for Excel spreadsheets.

Each file format contains data that is stored in a unique manner unlike other format types.  Your computer requires a specific software program, called a host application, capable of opening, interpreting and rendering the data stored in .WINMAIL.DAT files. If the host application wasn't installed properly, your PC will generate an error while trying to open WINMAIL.DAT files.

Host Application information for WINMAIL.DAT Files
File Extension Code:
File Extension Type:
E-mail related documents
Host Application Info:
Microsoft Outlook Use PC TuneUp Maestro to check if the host application was installed properly or not.
Download PC Tuneup Maestro to open unknown file extension.

Perform a quick scan of file extension related system issues to to identify if an improperly installed host application has caused errors when attempting to open .WINMAIL.DAT files.

Common Cause #2: Corrupt WINMAIL.DAT File Type Association

Another common cause of failing to open WINMAIL.DAT files is a corrupt Windows registry. The Windows registry is an internal database that stores information about the operating system itself and all software applications that have been installed on your PC. A large amount of data is constantly being read from and written to the Windows registry when your PC is running. Without proper maintenance, the Windows registry gradually becomes bloated and contains empty or erroneous entries.

More specifically, two types of errors can occur in the registry. The first type is caused by a mismatched file association. This occurs when a file type, such as “.WINMAIL.DAT”, is linked to a completely irrelevant host application. The second type of error is related to empty file paths.  These occur when your computer is directed to installation folder locations that do not exist.

Perform a quick scan of file type associations to discover issues in the registry that prevent opening DAT files.

How to Open WINMAIL.DAT Files:

1. Check and ensure a host application for WINMAIL.DAT files is installed properly. Use PC TuneUp Maestro to perform a quick scan of your PC's system registry to identify any installation errors that are occurring as a result of having an improperly installed host application for .WINMAIL.DAT files.

2. Perform a complete check of file associations in the Windows registry. To ensure that your computer is fully set up to open WINMAIL.DAT files, scan system registry entries of all file types and fix file association errors.

In both cases it is strongly recommended that you run a free scan to identify system registry errors.

Download instructions: Click the download PC TuneUp Maestro link. In the File Download dialog box, click Run and follow the steps provided by the installation wizard.

PC Tuneup Maestro is safe, secure and it is certified by Microsoft for being compatible with Windows 7. It also supports both Vista and XP.
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CompuClever, the maker of PC Tuneup Maestro software product, is the owner of the Microsoft Certified Partner logo.