Home » Docs » Glossary » MIME

MIME

What Is MIME?

MIME is a standard that allows emails to contain more than just plain text. It lets you include HTML formatting, images, attachments, and special characters in email messages.

Without MIME, emails would only support basic ASCII text. MIME extends email functionality so you can send rich content like styled HTML emails, PDF attachments, and text in different languages.

When you send emails through SendLayer, MIME formatting happens automatically behind the scenes.

Table of Contents

What Does MIME Stand For?

MIME stands for Multipurpose Internet Mail Extensions. It was created in the early 1990s to extend the capabilities of email beyond simple text messages.

Originally, email systems could only handle 7-bit ASCII characters. This meant you couldn’t send files, use special characters, or format your messages. MIME solved this problem by defining how to encode different types of content so they could be safely transmitted via email.

How Does MIME Work?

MIME works by adding special headers to email messages that describe the content type and structure. These headers tell email clients how to interpret and display the message.

When you send an email with both HTML and plain text versions, MIME creates a multipart message. Each part has its own content type header. The receiving email client then chooses which version to display based on its capabilities.

For attachments, MIME encodes the files (typically using Base64) and includes them as separate message parts. The Content-Type header identifies the file type, such as application/pdf for PDFs or image/jpeg for images.

Here’s a simple example of what MIME headers look like in an email:

MIME-Version: 1.0 
Content-Type: multipart/alternative; 
boundary="boundary-string" 

--boundary-string 
Content-Type: text/plain; 
charset="utf-8" This is the plain text version. 

--boundary-string
Content-Type: text/html; 
charset="utf-8" 
<html><body><p>This is the HTML version.</p></body></html> 
--boundary-string--

What Are MIME Types?

MIME types (also called media types or content types) identify the format of content in an email or on the web. They tell applications how to process and display the content.

A MIME type consists of two parts separated by a slash: a type and a subtype. Here are some common MIME types used in email:

  • text/plain – Plain text email content
  • text/html – HTML-formatted email content
  • application/pdf – PDF documents
  • image/jpeg – JPEG images
  • image/png – PNG images
  • application/json – JSON data
  • multipart/alternative – Email with multiple versions (HTML and plain text)
  • multipart/mixed – Email with attachments

When you use SendLayer to send emails with attachments, you can specify the MIME type for each file. This ensures that recipients’ email clients handle the attachments correctly.

That’s it! Now you know what MIME is and the most common MIME types used to send emails.

Ready to send emails with rich content? Check out these resources: