When Microsoft Outlook is not properly configured, attachments may sometimes be sent in the format of winmail.dat. This is a binary file format that can only be read by Microsoft Outlook and is basically useless to other applications. With a simple and free online service such as winmaildat.com, users can upload their .dat files, have the information and attachments extracted, download the resulting files, and open and view them.
Open a Web browser and navigate to winmaildat.com.
Click the "Browse" button and select the winmail.dat file.
Click the "Send file" button to upload the file.
Click on the "Results" tab to download the contents of the winmail.dat file.
The maximum size of your winmail.dat file cannot exceed 5 MB.