How do I open winmail.dat on my iPhone?

Save the attachment to Files, open this page in Safari, tap Choose files and pick it. The attachments inside are listed and you can download each one.

How do I open winmail.dat on Android?

Download the attachment, open this page in Chrome, tap Choose files and pick it from Downloads.

Do I need to install an app?

No. The opener runs in Safari or Chrome. There is nothing to install and no signup.

Is the file uploaded?

No. It is unpacked in your phone's browser and never sent to our server or stored.

What about ATT00001.dat?

It's usually the same thing under a different name. The opener checks the contents, so open it the same way.

Yes. No signup and no cap on the number of files.

Open winmail.dat on iPhone, iPad or Android

Why your phone shows winmail.dat

Winmail.dat is a container made by Microsoft Outlook on Windows when a message is sent in Outlook's Rich Text Format. Outlook packs the formatting and the attachments into this one file. Outlook on the receiving side unpacks it, but phone mail apps often can't, so you see winmail.dat (or ATT00001.dat, or a file with no name) and nothing else.

The documents and pictures are inside it. You just need something that can unpack it.

On an iPhone or iPad

Save the attachment. In Mail, touch and hold winmail.dat (or tap it and then the Share button) and choose Save to Files. Pick a folder you'll find again, such as Downloads or On My iPhone.
Open this page in Safari, then tap Choose files in the box above.
Tap Browse (or Choose File) and pick the winmail.dat you just saved.
Read the message and get the files. Each attachment is listed with its name and size. Tap Download next to a file; Safari saves it to Downloads in the Files app, and you can open or share it from there.

On an Android phone or tablet

Download the attachment. In Gmail or your mail app, tap the download icon on winmail.dat. It goes to your Downloads folder.
Open this page in Chrome and tap Choose files in the box above.
Pick winmail.dat from Downloads (or Recent).
Download the attachments you need. They land in Downloads and open in the usual apps.

If you'd rather have everything at once, tap Download all (ZIP). On a phone, single files are often easier to open than a ZIP.

Keep a copy of the message

Tap Save as PDF to open a print-ready version of the email. On an iPhone or iPad, use the print options to share or save it as a PDF in Files. On Android, choose Save as PDF as the printer.

Your email stays on your phone

The opener runs entirely in your browser. The winmail.dat file is unpacked on your phone and is never uploaded to our server or stored anywhere. Only this page and its scripts come from us. That's worth knowing, since these attachments are often contracts, invoices or personal photos.

If it doesn't work

You can't find the saved file. On iPhone, open the Files app and look in Recents. On Android, open the Files app and look in Downloads.
The file is very small (a few hundred bytes) and shows no attachments. Sometimes winmail.dat only carries formatting; the real attachments may be elsewhere in the email or missing. Ask the sender to send them again.
A document is password-protected. The opener gets it out, but you still need the password to open it.
Calendar invites appear as an .ics attachment that you can download and add to your calendar.

How to stop getting winmail.dat

The fix is on the sender's side. In Outlook for Windows they can go to File > Options > Mail and set Compose messages in this format to HTML or Plain Text. Until then, bookmark this page. On a computer? See the winmail.dat opener or how to open winmail.dat on a Mac.