What is Winmail
Winmail.dat files are attachments sent by Microsoft mail applications (Outlook, Outlook Express or Exchange) on a proprietary format called TNEF (transport neutral encapsulation format). Being a non-standard attachment format, users from other e-mail clients (like Gmail or Thunderbird) or platforms (like Android, Apple, iPad or iPhone) cannot natively read them.
An e-mail containing an winmail.dat attachment looks like an empty e-mail with only one attachment. The original e-mail information like subject, body and attachments is packed into a single winmail.dat file, which in some cases also receives a generic name like ATT00001.dat or ATT00005.eml.
How to open Winmail.dat files
Winmail.dat Reader is the only free application that decodes not only the embedded attachments but also the subject and body. It comes in three version:
- Winmail.dat Reader Online free decoder for all other platforms
- Winmail.dat Reader application for MS Windows
- Winmail.dat Reader application for Android
More information on what is a winmail.dat file
To learn more about winmail.dat files, check also these links:
- Microsoft Exchange – How to Prevent the Winmail.dat File from Being Sent
- Microsoft Outlook – How to Prevent the Winmail.dat File from Being Sent
- MozillaZine Knowledge Base – Winmail.dat attachments
- Wikipedia – Transport Neutral Encapsulation Format
Other native decoders
If you are looking for a Mac, iPhone, iPad or Linux solutions, check these ones: