What is a winmail.dat file?

winmail.dat is a TNEF (Transport Neutral Encapsulation Format) package created by Microsoft Outlook when sending rich-text or certain formatted emails. Non-Outlook clients (Gmail, Apple Mail, Thunderbird) often cannot open it and show a useless .dat attachment instead of the real files.

How do I open winmail.dat without Outlook?

Use a TNEF decoder. JustToolkit’s winmail.dat viewer runs in your browser: drop the file, extract attachments, and download them. No Outlook install and no account required.

Is it safe to open winmail.dat online?

This tool parses winmail.dat entirely in your browser with JavaScript. Your file is never uploaded to our servers, which is safer than many online converters that require a full upload.

Why did I receive winmail.dat in Gmail?

The sender used Outlook with TNEF/rich-text packaging. Gmail does not decode TNEF natively, so attachments appear as winmail.dat. Extract them with a TNEF viewer like this one.

Can this tool extract PDF and Word files from winmail.dat?

Yes. When attachments are stored in the TNEF stream, they are listed with their original filenames so you can download PDFs, Office documents, images, and other files.

Free & Private — No Upload, No Sign-in

Open winmail.dat Online
Extract TNEF Attachments Free

Got a useless winmail.dat from Outlook in Gmail or Apple Mail? Decode TNEF in your browser and download the real PDFs, Word files, and images — no Outlook required.

100% client-side — your file never leaves your device

Drop your winmail.dat file here

Drag & drop, or click Browse — TNEF is parsed locally

Supports: winmail.dat · .tnef · .dat · Max 50 MB · Free & unlimited

winmail.dat

0 KB

Decoding TNEF package…

Checking TNEF signature

Reading message attributes

Extracting attachments

Ready to download

Parse Error

Results

✓ Valid TNEF

First 256 bytes. Valid TNEF starts with signature 78 9F 3E 22 (0x223E9F78 little-endian).

100%

Private — Zero Upload

Software to Install

Always Free

All OS

Windows, Mac, Linux, Mobile

Simple Process

How to Open winmail.dat Online

Three steps — entirely in your browser

Drop winmail.dat

Save the attachment from Gmail, Apple Mail, or any client, then drop it here. No account needed.

Decode TNEF locally

We validate the TNEF signature and walk message + attachment attributes without sending data to a server.

Download real files

Get PDFs, Office docs, images, and other files with their original names when present in the package.

Why JustToolkit

Built for winmail.dat headaches

Outlook packaging vs. everyone else — we sit in the middle and unpack it cleanly

100% private

Parsing runs in JavaScript on your device. Ideal when attachments may contain contracts or HR docs.

No Outlook required

Works for Gmail, Apple Mail, Proton, Thunderbird, and mobile webmail users stuck with a .dat file.

Real TNEF parser

Checks signature 0x223E9F78 and walks TNEF attributes — not a fake rename of a generic file viewer.

Attachment downloads

Each embedded file can be saved individually with a sensible filename and MIME hint.

FAQ

winmail.dat questions

winmail.dat is Microsoft’s TNEF package. Outlook may wrap rich text and attachments into this single .dat file, which other email apps cannot open natively.

Use this free online TNEF decoder: drop the file, extract attachments, and download them. No Outlook installation is required.

No upload. Decoding runs entirely in your browser. Closing the tab clears in-memory data.

The sender used Outlook with TNEF packaging. Gmail cannot expand TNEF, so you only see winmail.dat instead of the real attachments.

Yes, when those files are stored as TNEF attachments they appear in the Attachments tab with download buttons.

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Open winmail.dat Online Extract TNEF Attachments Free