The answer to Mail multipart/alternative vs multipart/mixed suggests that attachments should be peers of the multipart/alternative message, like:

  • multipart/mixed
    • multipart/alternative
      • text/plain
      • text/html
    • some/thing (disposition: attachment)
    • some/thing (disposition: attachment)
    • ...

I'd like to send email with an html part with some inline images and a plain text alternative. What is the preferred MIME layout for the various parts? A couple of options appear in example code and in other questions, but which have worked best in practice? My inclination is this:

  • multipart/alternative
    • text/plain
    • multipart/related
      • text/html (referencing the images by cid)
      • image/gif
      • image/gif
      • ...

That way, the images are clearly for the purpose of rendering the html part. A full example of this would be:

From: Rich Example <rich-example@example.org>
To: A Recipient <recipient@example.org>
Subject: An example of email with images and a plain alternative
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="outer-boundary"

This is a MIME-encoded message. If you are seeing this, your mail
reader is old.
--outer-boundary
Content-Type: text/plain; charset=us-ascii

This message might make you :) or it might make you :(

--outer-boundary
MIME-Version: 1.0
Content-Type: multipart/related;
  type="text/html"; start="<body@here>"; boundary="inner-boundary"

--inner-boundary
Content-Type: text/html; charset=us-ascii
Content-Disposition: inline
Content-ID: <body@here>

<html>
 <body>
  This message might make you
  <img src="cid:smile@here" alt="smile">
  or it might make you
  <img src="cid:frown@here" alt="frown">
 </body>
</html&g
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