Multipart MIME cheat sheet

I’ve had a couple of people ask me about MIME structure recently, especially how you create multipart messages, when you should use them and which variant of multipart you use for different things. (And I’m working on a MIME parser / generator for Abacus at the moment, so it’s all fresh in my mind)
So I’ve put together a quick cheat sheet, showing the structure of four common types of email, and how their MIME structure looks.

Simple plain text

text/plain

Plain text with a PDF attachment

multipart/mixed

text/plain
application/pdf

HTML with a plain text fallback

multipart/alternative

text/plain
text/html

HTML with embedded images and plain text fallback

multipart/alternative

text/plain
multipart/related

text/html
image/gif
image/gif
image/jpeg
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