What is MIME type "application/vnd.ms-tnef"?

A MIME type is a string that tells browsers and other tools how to handle a particular kind of file.

application/vnd.ms-tnef is a MIME type for Microsoft's Transport Neutral Encapsulation Format. It is used to wrap complex email content, including formatting details, metadata, and attachments into one file.

Email messages from Microsoft Outlook or Exchange often use this format. It bundles multiple parts—such as rich text formatting and embedded files—into a single stream. Non-Microsoft systems may not render these details correctly because they handle the format differently.

Files that contain this MIME type commonly appear with extensions such as DAT and TNEF.

Encapsulation: Combines email formatting, metadata, and attachments in one package.
Microsoft Integration: Primarily used by Microsoft Outlook and Exchange to maintain message integrity.
Complexity: Handles rich text and multiple attachments in a single container.
Interoperability Issues: May not display correctly in non-Microsoft email clients.

For additional details on the format, refer to Wikipedia.

Associated file extensions

.dat, .tnef

Usage Examples

HTTP Header

When serving content with this MIME type, set the Content-Type header:


    Content-Type: application/vnd.ms-tnef

HTML

In HTML, you can specify the MIME type in various elements:


    <a href="file.dat" type="application/vnd.ms-tnef">Download file</a>

Server-side (Node.js)

Setting the Content-Type header in Node.js:


    const http = require('http');
    
    http.createServer((req, res) => {
      res.setHeader('Content-Type', 'application/vnd.ms-tnef');
      res.end('Content here');
    }).listen(3000);

Associated file extensions

.dat, .tnef

FAQ

What is a MIME type?

A MIME (Multipurpose Internet Mail Extensions) type is a standard that indicates the nature and format of a document, file, or assortment of bytes. MIME types are defined and standardized in IETF's RFC 6838.

MIME types are important because they help browsers and servers understand how to process a file. When a browser receives a file from a server, it uses the MIME type to determine how to display or handle the content, whether it's an image to display, a PDF to open in a viewer, or a video to play.

MIME types consist of a type and a subtype, separated by a slash (e.g., text/html, image/jpeg, application/pdf). Some MIME types also include optional parameters.

How do I find the MIME type for a file?

You can check the file extension or use a file identification tool such as file --mime-type on the command line. Many programming languages also provide libraries to detect MIME types.

Why are multiple MIME types listed for one extension?

Different applications and historical conventions may use alternative MIME identifiers for the same kind of file. Showing them all helps ensure compatibility across systems.