Winmail.dat Viewer & Extractor
Open winmail.dat files from Microsoft Outlook. View email content and extract attachments — all in your browser, nothing uploaded.
Your files stay safe — processed entirely in your browser. Nothing is uploaded.
Drop winmail.dat file here
or click to select a file
Supports winmail.dat files (TNEF format).
How to Open winmail.dat Files
If you've ever received an email with a mysterious attachment called "winmail.dat", you're not alone. This file is created by Microsoft Outlook when it sends emails using a proprietary format called TNEF (Transport Neutral Encapsulation Format). Non-Outlook email clients like Gmail, Apple Mail, and Thunderbird can't decode this format, leaving you with an unopenable attachment.
Our winmail.dat viewer extracts the original email content and attachments right in your browser. The file is parsed locally using our custom-built TNEF decoder — nothing is uploaded to any server, so your email content stays completely private.
Select Your winmail.dat File
Drag and drop your winmail.dat file onto the upload area, or click to browse and select it from your device. Only one file is processed at a time.
View Email Content
The tool automatically parses the file and displays the email subject, sender information, and message body. If the email contains HTML formatting, you can toggle between plain text and HTML views.
Download Attachments
All attachments embedded in the winmail.dat file are listed with their file names, sizes, and types. Download each file individually, or use the "Download All as ZIP" button to get everything in a single archive.
The parsing process is nearly instant for typical winmail.dat files. Since all processing happens locally in your browser using our custom TNEF parser, your email data — including any sensitive attachments — never leaves your device. You may also see this attachment written as win.dat, windat, "win mail dat" or ATT00001.dat depending on the mail client that delivered it — they are all the same TNEF file and this tool opens all of them.
How this winmail.dat viewer works
No JavaScript library decodes TNEF in the browser, so the parser behind this tool was written from scratch in TypeScript. That is why the file can stay on your device — there is no server step to fall back on.
TNEF is a flat sequence of attribute records. The parser reads the 0x223e9f78 signature, then walks each record's level, attribute id, length and payload.
- Message attributes it reads
- attSubject (0x8004), attFrom (0x8000, skipping the TRP header), attBody (0x800c) and the MAPI property block (0x9003). Unicode values from the MAPI block take priority over the legacy ANSI copies, which is what keeps accented and non-Latin subjects intact.
- Attachment attributes it reads
- attAttachRendData (0x9002) opens each attachment, then attAttachTitle (0x8010) and attAttachData (0x800f) supply the legacy name and bytes, with the per-attachment MAPI block (0x9005) carrying the better filenames.
- Filename resolution order
- PidTagAttachLongFilename (0x3707), then PidTagAttachFilename (0x3704), then PidTagDisplayName (0x3001), and only then the legacy ANSI attAttachTitle. Tools that read just the legacy field are the ones that turn Japanese filenames into mojibake.
- Character encoding
- The OEM codepage attribute (0x9007) is read first and decides how every following ANSI string is decoded — Shift_JIS (932), GBK, EUC-KR, Big5, the Windows-125x family or UTF-8. MAPI strings are decoded as UTF-16LE.
- HTML email safety
- An HTML body from a stranger is untrusted input. It is sanitized with DOMPurify against an explicit tag and attribute allowlist, then rendered inside a sandboxed iframe so it cannot reach the surrounding page.
Where it stops
Encrypted or signed S/MIME payloads inside a TNEF container are not decoded, and because everything runs in a tab, a very large winmail.dat on a low-memory phone is bounded by that device's memory rather than by a server.