Open winmail.dat and any other .dat file right in your browser - no Outlook, no upload. Get the attachments out with their real names, read the message, and see what is really inside a mystery .dat file. Whole emails open in the EML & MSG Viewer, Outlook mailboxes in the PST Viewer.
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Several winmail.dat files at once? Drop them together and switch between them with the chips above the message.
Files come out with their real long names - PDFs, Word and Excel files, pictures - and save one by one or all at once as a ZIP.
Subject, sender, recipients, date and the formatted rich text or HTML body, with inline pictures in place.
Outlook meeting requests show their time and place, and save as an .ics file for any calendar app.
Turn the unpacked message into a standard .eml email that Thunderbird, Apple Mail and Gmail can open.
Video CD files, renamed pictures, PDFs, archives, databases and text are recognised by their content, not their name.
AVSEQ01.DAT files from Video CDs are turned into a clean .mpg video that VLC and other players open.
A fast hex view for any file, plus every TNEF attribute and MAPI property for the curious.
Nothing is uploaded, scripts in messages never run, and remote images stay blocked until you allow them.
A winmail.dat file is an Outlook package in TNEF format (Transport Neutral Encapsulation Format).
Outlook creates it when a message is written in Rich Text format and sent to someone outside the sender's Exchange organisation.
The package holds the formatting, the message properties and - the annoying part - the real attachments. Outlook unpacks it without you noticing, but Gmail, Apple Mail, Thunderbird and phone mail apps only see one file called winmail.dat (sometimes ATT00001.dat or noname.dat).
That is why the PDF or spreadsheet you were promised seems to be missing. It is inside the winmail.dat, and this viewer gets it out.
DAT is short for "data", and it is one of the most generic extensions there is.
There is no single DAT format - the content decides what the file is and which program opens it.
The viewer looks at the first bytes of the file, so it can tell you what you have even when the name gives nothing away.
| File | What it is | How to open it |
|---|---|---|
| winmail.dat, ATT00001.dat | Outlook TNEF package with the message and attachments | This viewer, or Outlook for Windows |
| AVSEQ01.DAT, MUSIC01.DAT | Video CD (VCD) MPEG-1 video in CD sectors | This viewer (save as .mpg), then VLC |
| level.dat, playerdata | Game save data, often compressed (Minecraft uses gzip NBT) | The game itself, or an NBT editor |
| settings.dat, config.dat | Program settings, often plain text | This viewer, or the TXT Viewer |
| Renamed files | A PDF, picture or ZIP whose extension got lost | This viewer saves it with the right extension |
This viewer runs in the browser, so the steps are the same on every device: open this page and pick the file.
Here is what each system offers on its own.
Windows has no built-in app for winmail.dat, and double-clicking it usually asks which program to use. Outlook decodes it only when the original email is opened in Outlook, not the saved .dat file.
Drop the file here instead - the attachments are out in seconds, nothing to install.
Apple Mail shows winmail.dat as a plain attachment and macOS cannot open it. Save it to your Downloads folder, open this page in Safari or Chrome and drop it in.
Press and hold the winmail.dat attachment in Mail and choose Save to Files. Then open this page in Safari, tap the drop area and pick it from Files.
Download the attachment from Gmail or your mail app, open this page in Chrome, tap the drop area and choose winmail.dat from Downloads.
Every conversion happens in your browser, from the buttons under the file.
Got a ZIP out of it? Look inside with the ZIP Viewer. A raw binary file? The Hex Viewer has more room to dig.
The fix is on the sender's side - the person or company using Outlook.
Set-RemoteDomain Default -TNEFEnabled $false so outside recipients never get TNEF.Until then, keep this page bookmarked - it is the quickest way to get the files out.
The viewer checks every file and names the problem. These are the usual suspects:
More formats? Browse all file viewers.
Drop the winmail.dat file onto this page or click the drop area to pick it. The viewer unpacks it in your browser and shows the message text and every attachment inside, ready to preview or download.
It works on Windows, Mac, iPhone, Android and Chromebooks with nothing to install.
The sender used Microsoft Outlook with the Rich Text format. Outlook then packs the formatting and the attachments into one TNEF file called winmail.dat, which only Outlook understands.
Gmail, Apple Mail, Thunderbird and phones show it as a mystery attachment instead.
Yes. The file is read by your own browser and never uploaded.
The message is shown in a locked frame where scripts cannot run, and the attachments are only saved when you click them, so check them like any other email attachment.
DAT simply means "data", so many different programs use it: Outlook (winmail.dat), Video CDs (AVSEQ01.DAT), games such as Minecraft (level.dat) and countless apps for settings.
Drop it here and the viewer checks what is really inside, then shows it as an email, picture, video, text or hex dump.
A .dat file is usually a container, not a document. Open it here and save what is inside: winmail.dat attachments keep their real names and formats (PDF, DOCX, XLSX, JPG).
If the .dat file is really a renamed PDF, picture or ZIP, the viewer recognises it and saves it with the right extension.
Yes. Save the winmail.dat attachment to Files (iPhone) or Downloads (Android), open this page in Safari or Chrome and tap the drop area to pick it.
The attachments open or download straight on your phone.
In Outlook, go to File - Options - Mail and set Compose messages in this format to HTML. In the same window, under Message format, set the Rich Text option to Convert to HTML format.
Microsoft 365 admins can turn TNEF off for outside domains with Set-RemoteDomain Default -TNEFEnabled $false.
Some winmail.dat files only carry formatting and no attachments - then the viewer shows just the message text. A file of a few bytes, or one that stops in the middle, was cut off while saving; the viewer opens everything before the cut and tells you so.
Save the attachment again from the original email if files are missing.