What Is MIME in Email?

What Is MIME in Email?

MIME (Multipurpose Internet Mail Extensions) is a standard that extends email format to support attachments, non-ASCII characters, and multiple content types. MIME enables emails to include: HTML content, plain text content, attachments (files), images, and other binary data.

MIME format includes: MIME headers (Content-Type, Content-Disposition, Content-Transfer-Encoding), MIME boundaries (separating parts), content types (text/html, text/plain, application/pdf, etc.), and encoding methods (Base64, quoted-printable). MIME allows emails to contain multiple parts (multipart messages) and supports rich content beyond plain text.

MIME is essential for modern email communication. Learn more about multipart emails and MIME structure.

MIME Format

MIME Headers

MIME headers specify content type, disposition, encoding, and other MIME information:

• Content-Type: Specifies content type (text/html, text/plain, application/pdf, etc.)
• Content-Disposition: Specifies how content should be handled (inline, attachment)
• Content-Transfer-Encoding: Specifies encoding method (base64, quoted-printable)
• Content-ID: Unique identifier for inline attachments

MIME Boundaries

MIME boundaries separate different parts of multipart emails. Boundaries are unique strings that mark the start and end of each part.

MIME Structure

MIME structure organizes email content into parts, each with its own headers and content.

MIME Structure

MIME structure organizes email content:

Single Part Messages

Simple emails with one content type (text/plain or text/html) use single part MIME structure.

Multipart Messages

Emails with multiple parts (HTML + plain text + attachments) use multipart MIME structure. Learn more about multipart emails.

MIME Boundaries

MIME boundaries separate parts in multipart messages, allowing email clients to identify and parse different parts.

Part Structure

Each MIME part contains: MIME headers (Content-Type, etc.), blank line, and part content (encoded if needed).

Content Types

MIME content types specify the type of content in each part:

Text Content Types

• text/plain: Plain text content
• text/html: HTML content
• text/css: CSS stylesheets

Image Content Types

• image/jpeg: JPEG images
• image/png: PNG images
• image/gif: GIF images

Application Content Types

• application/pdf: PDF files
• application/zip: ZIP archives
• application/octet-stream: Binary files

Multipart Content Types

• multipart/alternative: HTML and plain text alternatives
• multipart/mixed: Mixed content (text + attachments)
• multipart/related: Related content (HTML + inline images)

MIME Encoding

MIME encoding converts binary data to text for email transmission:

Base64 Encoding

Base64 encoding converts binary data (images, attachments) to ASCII text for email transmission. Commonly used for attachments and images.

Quoted-Printable Encoding

Quoted-printable encoding encodes non-ASCII characters in text content, making them safe for email transmission.

7-bit Encoding

7-bit encoding is used for plain ASCII text that doesn't require encoding.

8-bit Encoding

8-bit encoding is used for text with non-ASCII characters when quoted-printable encoding is used.

Encoding Purpose

MIME encoding ensures binary data and non-ASCII characters can be transmitted safely in email messages.