Open a winmail.dat file

What winmail.dat is

winmail.dat (sometimes ATT00001.dat, or a file with no clear name) is a package made by Microsoft Outlook and Exchange. Its proper name is TNEF, Transport Neutral Encapsulation Format. When Outlook sends an email in its own “rich text” format to someone whose email program doesn’t speak it, the formatting and the attachments are bundled into this one file. Apple Mail, Gmail and most phone mail apps don’t unpack it, so you see winmail.dat instead of the PDF or photo you were expecting.

How to unpack it

1. Save the winmail.dat attachment from your email.
2. Drop it on this page, or press Choose a file.
3. The files inside appear in the attachment list. Press Save on each one you want.

If the package holds the message text (it often does, as rich text), that’s shown on the page too, along with the subject and sender when they’re included.

Got the whole email as an .eml?

You can also open the complete email, saved as .eml, with the winmail.dat still attached. The page unpacks the winmail.dat automatically and lists the files inside it under the attachment, and if the email itself looked empty, it shows the message from inside the package instead.

Private by design

Popular winmail.dat sites work by uploading your file to their server and unpacking it there. This page doesn’t: the unpacking happens in your browser, on your computer or phone. That matters, because winmail.dat files tend to carry exactly the things you’d rather not hand to a stranger: contracts, invoices, scans of ID, payslips.

What can be inside

• Attachments with their original names, such as PDFs, Word and Excel files, and photos.
• The message, stored as compressed rich text or HTML, which is turned back into readable text.
• Attached emails, which you can open in turn.
• Calendar invitations from Outlook, whose details are shown as text.

When there’s nothing useful inside

Sometimes a winmail.dat only carries formatting: the text and attachments already arrived normally, and the package just repeats the rich-text version. In that case the page shows whatever is in it, which may only be the message text. If the file is cut short, the page says so and shows what could be recovered.