Free winmail.dat opener & viewer

When someone writes an email in Microsoft Outlook with the message format set to Rich Text — common in offices running an Exchange server — Outlook doesn't attach files the normal way. Instead it packs the attachments, the text formatting, and some Outlook-only extras into a single container file in a Microsoft format called TNEF, and names it winmail.dat.

If you read that email in Outlook, the container is unpacked invisibly and you never notice. In anything else — Gmail, Apple Mail, your iPhone, Thunderbird — you just see one useless-looking attachment where the real files should be. Nothing was lost: the document you were promised is sitting inside the winmail.dat, and this page gets it out. Sometimes the file even arrives renamed to something like ATT00001.dat; it decodes the same way.

You don't need to install anything, and you don't need Outlook. Save the winmail.dat attachment from the email to your device, drop it into the box at the top of this page, and download the files inside — individually or as one .zip. It works on Windows, Mac, iPhone, iPad, Android, and Linux, because the decoding runs in your browser and your file is never uploaded.

One thing to check first: if the mystery attachment ends in .eml rather than .dat, it's a complete forwarded email in the standard format, not TNEF — open it with our free EML viewer instead (here's what a .eml file is, if you're curious).

The cause is on the sender's side, so the permanent fix is too. Ask the sender to make one small change in Outlook: File → Options → Mail, then set “Compose messages in this format” to HTML or Plain Text instead of Rich Text. From then on, their attachments arrive normally for everyone.

If they only want to fix it for you: in their Outlook, they can open your contact card, double-click your email address, and set “Internet format” to “Send Plain Text only” — Outlook remembers the setting per recipient. And if the emails come from a whole company, their Exchange administrator can switch off TNEF for outbound internet mail in one command (Set-RemoteDomain -TNEFEnabled $false).

Until one of those happens, there's no setting on the receiving side that prevents it — you can only decode the files as they arrive, which is what this page is for.

Three kinds of things. First, the attachments — the PDFs, documents, and images the sender actually meant to send; this is what most people are after, and this tool extracts them byte-for-byte. Second, the message's Rich Text formatting — fonts, colors, layout. Third, Outlook-specific data that only makes sense to Outlook: meeting requests and calendar invites, voting buttons, task requests, and contact cards. This viewer pulls out the attachments and any readable message text; the deeply Outlook-only parts have no useful form outside Outlook.