What is the difference between plain text and HTML body parts?

Plain text is the barebones version of an email: no formatting, no images, just the message itself. HTML, on the other hand, allows for layout, colors, links, and design.

When both are included in a multipart/alternative email, the email client decides which version to display based on user settings or compatibility, not the retrieval protocol. This ensures recipients can view your message even if their client cannot render HTML.