FAQ
Answers before you start.
A few practical notes about Outlook’s winmail.dat files and this browser-based decoder.
Why did I receive a winmail.dat file?
Microsoft Outlook can package rich-text formatting, calendar details, and attachments using Transport Neutral Encapsulation Format (TNEF). Mail apps that do not understand TNEF often show the package as winmail.dat.
Does this support ATT0001.dat?
Yes. ATT0001.dat is another filename commonly used for a TNEF attachment. Select or drop it into the decoder just like winmail.dat.
Is my file uploaded?
No. The selected file is read and decoded in your browser. The application does not need to upload the file contents to recover the attachments.
What file size can I use?
The decoder accepts DAT files up to 150 MB. This keeps local processing responsive and limits memory pressure on phones and older devices.
Why did the tool find no attachments?
The file may be incomplete, may only contain formatting metadata, or may not actually be a TNEF container. Downloading the original attachment again is the best first retry.
Can I download everything together?
Yes. After a successful decode, choose Download all to create a ZIP in your browser. Individual download links are also available for each recovered file.