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.
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Click the "Send file" button to upload the file.
Click on the "Results" tab to download the contents of the winmail.dat file.