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

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

The application/vnd.ms-outlook MIME type tells software how to handle Outlook data files. It lets Microsoft Outlook save and share emails and other communications in its own formats.
It is the backbone for storing and archiving email content and related data.

Email storage: Individual messages are saved in MSG files.
Data archives: Entire mailboxes and folders are backed up in PST files.
Offline access: A local copy of a mailbox is kept in OST files.
Message templates: Predefined emails use OFT files.
Legacy support: Older Outlook versions use formats like NST and PAB to store personal folder data.

This MIME type ensures that Outlook and compatible programs read the file correctly. For more details on MIME types, see the MIME article.

Associated file extensions

.msg, .pst, .ost, .oft, .nst, .pab

Usage Examples

HTTP Header

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


    Content-Type: application/vnd.ms-outlook

HTML

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


    <a href="file.dat" type="application/vnd.ms-outlook">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-outlook');    
      res.end('Content here');    
    }).listen(3000);

Associated file extensions

.msg, .pst, .ost, .oft, .nst, .pab

FAQs

How do I open a file with the application/vnd.ms-outlook MIME type?

You typically need Microsoft Outlook installed on your computer to open these files properly. Since web browsers cannot render this binary format natively, they will download the file (usually with a .msg or .pst extension) for you to open locally.

Why does my browser download .msg files instead of displaying them?

Browsers like Chrome, Firefox, and Edge do not have built-in engines to parse proprietary Microsoft Outlook formats. When a server sends the application/vnd.ms-outlook header, the browser triggers a download so the user can open the file in a compatible desktop application.

How do I configure Apache to serve Outlook files correctly?

To ensure correct handling, add the MIME type directive to your .htaccess file or main configuration. Use the line: AddType application/vnd.ms-outlook .msg .pst .ost. This ensures the server tells the client exactly what type of data is being transferred.

What is the difference between application/vnd.ms-outlook and message/rfc822?

application/vnd.ms-outlook is used for Microsoft's proprietary binary format (like .msg), which supports complex Outlook-specific objects. In contrast, message/rfc822 is used for standard, text-based email files (like .eml) which are compatible across many different email clients.

Are there security risks associated with Outlook data files?

Yes, files associated with this MIME type, particularly .msg, can contain malicious macros or embedded scripts. It is important to scan these files for malware before opening them, especially if they arrive as attachments from unknown sources.

Can I open application/vnd.ms-outlook files on a Mac or Linux machine?

While the format is native to Windows, you can open these files on macOS using Outlook for Mac. On Linux, you may need to use command-line tools like msgconvert to transform the file into a standard standard format, or use third-party viewer applications.

What should I do if my server returns application/octet-stream for .msg files?

This is a generic binary stream header and often means the server isn't configured for Outlook files. You should update your web server's MIME map to associate .msg with application/vnd.ms-outlook to prevent client-side confusion.

General 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.