Got winmail.dat Instead of the Attachment?
Your files are inside it. Here's how to get them out, and how the sender stops it.
The Short Answer
winmail.dat is a package, not a broken file. When someone sends from Outlook in Rich Text format, Outlook wraps the message and its attachments into one file in Microsoft's TNEF format. If your mail app doesn't unpack TNEF, you see winmail.dat instead of the PDF.
Your PDF is inside it. You can get it out on your iPhone in a minute, and the sender can change one setting so it stops happening.
Open winmail.dat →Get the Files Out on iPhone
Safari can't reach inside the Mail app, so first save a copy of the winmail.dat to Files.
- In Mail, open the email. Touch and hold the winmail.dat attachment, then choose Save to Files and pick where to save it.
- Open the Email File Opener in Safari.
- Tap the file picker, browse to where you saved it, and choose winmail.dat.
- The files that were packed inside are listed with their real names. Tap Download next to the one you want, or Download all (.zip) for everything.
- Safari saves downloads to the Downloads folder in the Files app by default. Open the PDF from there.
As an example, a sample winmail.dat from the Apache POI project's test files opens to show five files: quick.doc, quick.html, quick.pdf, quick.txt and quick.xml, each with its own Download button.
The file is read on your phone and never uploaded. That's worth having here: Microsoft notes that a winmail.dat can also contain the sender's sign-in name and the path of their Outlook data file.
Why It Happens
Outlook can send a message in three formats: HTML, Plain Text or Rich Text. HTML is the default and works everywhere. Rich Text is the one that causes this. Microsoft's own explanation: Outlook packages a Rich Text message with TNEF, and if the recipient's system can't process that format, an attachment named winmail.dat is added.
So nothing is wrong on your side, and nothing was lost. The sender's Outlook used Rich Text, either as its setting for every email or just for that one message.
What the Sender Can Change
Forward these steps to the person who sent it. They come from Microsoft's support article on TNEF, for classic Outlook for Windows.
- For every email: File → Options → Mail. Under Compose messages in this format, choose HTML (or Plain Text) and select OK.
- For one email: on the Format Text tab, select Message Format and choose HTML or Plain Text before sending.
- For a whole company on Exchange Online: an admin can set the remote domain's Use Rich-text format option to Never in the Exchange admin center, or run
Set-RemoteDomain -TNEFEnabled $false. Rich Text messages to outside addresses are then sent as HTML or plain text.
Microsoft notes some Outlook features still use TNEF whatever the setting, such as meeting requests and voting buttons. Ordinary attachments don't need it.
Things That Trip People Up
- It's called ATT00001.dat. Some mail apps give the package a generic name such as ATT00001.dat. It's the same thing and opens the same way.
- The message text is missing. Often the readable text arrives in the email itself and winmail.dat holds the formatted copy. If the winmail.dat only has a Rich Text body, the opener shows it as plain text, without fonts or colours.
- Forwarding doesn't help. Forwarding the email to yourself sends the winmail.dat along with it. Open it, or ask for a resend.
- You saved the whole email instead. If you have an .eml file with winmail.dat inside, open that in the same tool and tap Open next to winmail.dat.
- It's a meeting invite. Outlook sends meeting requests with TNEF on purpose. The opener shows the text and any attachments, but not a calendar entry.
On Android, Mac or Windows
The same tool works in any modern browser. Save the winmail.dat attachment from your mail app, open the Email File Opener, and choose the file. On a computer, it ends up in your usual Downloads folder.
If the sender also sent you an Outlook .msg file, see how to open a .msg file without Outlook.
Frequently Asked Questions
Why do I get winmail.dat instead of a PDF?
The sender's Outlook sent the message in Rich Text format. Outlook then packs the formatted text and the attachments into one file in Microsoft's TNEF format, usually named winmail.dat. Mail apps that don't understand TNEF show that package instead of the PDF. The PDF is inside it.
How do I open winmail.dat on iPhone?
Save it to the Files app: in Mail, touch and hold the attachment and choose Save to Files. Then open the Email File Opener on fairtoolbox.com in Safari, choose the saved file, and tap Download next to the file you want.
Is winmail.dat a virus?
No. It's a normal Microsoft format for packaging an Outlook message. Like any attachment, though, the files inside it can be anything, so only open files you were expecting from someone you know.
How does the sender stop sending winmail.dat?
In classic Outlook for Windows, Microsoft's fix is File > Options > Mail, then set Compose messages in this format to HTML or Plain Text. For a single message, the Format Text tab has a Message Format option. An Exchange Online admin can also stop Rich Text format going to outside addresses for the whole organisation.
What is ATT00001.dat?
The same thing with a different name. Microsoft notes that when a mail app doesn't recognise the TNEF part or the winmail.dat name, it may make up a generic name such as ATT00001.dat. It opens the same way.
Will forwarding the email to myself fix it?
Usually not. The winmail.dat travels with the forwarded message, and your mail app still can't unpack it. Either open the winmail.dat with a TNEF reader, or ask the sender to resend after changing the format.