Guide

How to open a winmail.dat attachment on iPhone

An email arrived with a winmail.dat file and the attachments you expected are missing. They are inside it. Here is how to get them out.

Get EML & MSG Viewer on the App Store

What winmail.dat is

winmail.dat is a TNEF file (Transport Neutral Encapsulation Format). Outlook and Exchange produce it when a message is sent in Rich Text Format: instead of attaching each file normally, they bundle the formatting, the real attachments and sometimes a meeting request into one container that only Outlook understands. Recipients on any other mail program see a single winmail.dat, sometimes named ATT00001.dat, and nothing else. The files the sender meant to send are inside it.

Why Mail and Files cannot show it

iOS Mail does not decode TNEF, so it shows winmail.dat as a generic attachment with no preview. Files has no handler for .dat either; tapping it offers nothing but a share menu. Nothing is wrong with the file, and asking the sender to resend is not the only option.

Three ways to open it

  1. Share sheet. In Mail, tap the winmail.dat attachment, tap the Share button, and choose EML & MSG Viewer from the app row. The app unpacks the container and lists the attachments inside, with the meeting details when there is an invitation.
  2. Files. Save the file first (Share, then Save to Files). In Files, tap it; if Files does not open it directly, long-press the file, choose Share, then pick EML & MSG Viewer.
  3. AirDrop. If the message is on a Mac, AirDrop the winmail.dat to your iPhone or iPad and choose EML & MSG Viewer when iOS asks which app should receive it.

Opening, reading, saving attachments, headers and folder scan are free; PDF export is the one paid feature.

If it still will not open

Not every .dat is TNEF. If the app reports that the file is not a TNEF container, it is other data the sender named .dat, and they need to send it another way. If one person keeps sending winmail.dat, the fix is on their side: set Outlook's message format to HTML or plain text, or have their Exchange administrator turn off TNEF for outside recipients. A .pst, .ost or .olm file is a whole mailbox; this app does not open those, nor .mht or .xps. Ask for the single message exported from Outlook as .msg, or from Gmail via Download message (.eml). Still stuck? Email support with your iOS and app versions.

Questions

Why do I keep getting winmail.dat from one sender?

Their Outlook is sending in Rich Text Format, or their Exchange server is set to send TNEF to outside addresses. Only they or their administrator can change that. Until then, the app can unpack each one.

Will the meeting invitation inside show up?

Yes. When the winmail.dat carries a meeting request, the app shows the meeting details alongside any attachments.

Can I save the extracted attachments to Files or share them?

Yes. Each extracted attachment can be previewed with Quick Look, shared to another app, or saved to Files like any other file.