What is MIME type "message/rfc822"?

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

message/rfc822 defines the format for electronic messages that follow the standards of RFC 822.
It encapsulates the entire email, including headers, body, and attachments. File types that use this MIME type include EML, MHT, MHTML, and MIME.

Main use: Storing and exchanging complete email messages.
Key fact: It preserves sender, recipient, subject, date, and message body details.
Use cases: Archiving emails, transferring messages between systems, and rendering messages correctly in email clients.
Practical benefit: Ensures email content is processed as intended by software.

This MIME type is essential for accurate email presentation and data integrity.

Associated file extensions

.eml, .mht, .mhtml, .mime

Usage Examples

HTTP Header

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


    Content-Type: message/rfc822

HTML

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


    <a href="file.dat" type="message/rfc822">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', 'message/rfc822');    
      res.end('Content here');    
    }).listen(3000);

Associated file extensions

.eml, .mht, .mhtml, .mime

FAQs

What is the primary purpose of the message/rfc822 MIME type?

The message/rfc822 MIME type represents a complete electronic mail message, including all headers (like Subject, From, and Date) and the message body. It is the standard format used when saving individual emails as files, most commonly seen with the .eml extension.

How do I configure Apache to serve .eml files correctly?

To ensure your web server identifies email files correctly, add the line AddType message/rfc822 .eml to your .htaccess file or main Apache configuration. This helps the user's browser understand that the file should be handled by an email client rather than displayed as plain text.

Can web browsers display message/rfc822 content natively?

Generally, no; most modern web browsers will download the file rather than rendering it. Because message/rfc822 contains raw email headers and potentially multipart boundaries, browsers rely on external applications like Microsoft Outlook, Thunderbird, or Apple Mail to display the content properly.

What is the correct Nginx configuration for this MIME type?

In your nginx.conf file, locate the types { ... } block and ensure it includes message/rfc822 eml;. This mapping ensures that when a user requests an .eml file, Nginx sends the correct Content-Type header.

Are there security risks associated with opening message/rfc822 files?

Yes, files with this MIME type can contain the same threats as live emails, including malicious HTML, scripts, or infected attachments. You should treat downloaded .eml or .mime files with the same caution as an email in your inbox and scan them before opening.

Why is it called rfc822 if the standard has been updated?

Although the original RFC 822 standard was superseded by RFC 2822 and subsequently RFC 5322, the MIME type identifier message/rfc822 remains the standard IANA registration. Software and servers continue to use this string to maintain backward compatibility for identifying email data.

What is the difference between text/plain and message/rfc822?

While text/plain represents unstructured raw text, message/rfc822 implies a specific structure containing headers and a body. Software processing message/rfc822 will attempt to parse fields like Sender and Recipient, whereas text/plain is simply displayed as-is.

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.