Open Winmail.dat Files. The best way to open and view winmail.dat attachments online.

What are Winmail.dat Files?

Winmail.dat files are email attachments created by Microsoft Outlook when sending emails in Rich Text Format (RTF) to recipients who don't use Outlook. These files contain the original email's formatting, attachments, and metadata in Microsoft's proprietary TNEF (Transport Neutral Encapsulation Format).

When you receive a winmail.dat attachment, it typically means the sender used Microsoft Outlook or Exchange Server, and your email client can't interpret the special formatting and attachments embedded within the file.

How do I open a Winmail.dat file online?

1. Go to the Winmail Viewer page.
2. Drag and drop your winmail.dat file into the window, or click “Open File…” to select it from your device.

The tool will automatically extract and display the original email message and any attached files.

Data Protection: All processing takes place in your browser — your files never leave your device.

Why Choose Letter Opener for Winmail.dat Files?

• Instant Processing: Open winmail.dat files immediately without waiting for uploads or downloads
• Complete Privacy: All processing takes place in your browser — your files never leave your device.
• No Software Required: Works in any modern web browser without installing applications
• Extract Everything: Access embedded attachments, images, and formatted text content
• Cross-Platform: Works on Windows, Mac, Linux, iOS, and Android devices

Common Winmail.dat Issues Solved

Can't Open Winmail.dat on Mac or iPhone

Apple Mail and other non-Microsoft email clients display winmail.dat as an unreadable attachment. Letter Opener works perfectly on all Apple devices and browsers.

Missing Attachments in Emails

When attachments appear as winmail.dat instead of the original files, use Letter Opener to extract and download the embedded documents, images, or other files.

Corrupted Email Formatting

Letter Opener preserves the original Rich Text formatting, fonts, colors, and layout from Microsoft Outlook emails.

Technical Details

Winmail.dat files use Microsoft's TNEF (Transport Neutral Encapsulation Format) to preserve Rich Text Format (RTF) content and embedded objects. Our web-based decoder processes these files using WebAssembly technology for maximum performance and security.

Compatible with winmail.dat files from all versions of Microsoft Outlook, Exchange Server, and other MAPI-compliant email systems.