What is a Multipart MIME message?

A multipart MIME message is an email that consists of both a text part and an HTML part. When a recipient receives a multipart MIME message, their email reader should display the appropriate part based on the capabilities of the reader.

Most desktop and Web-based email readers are HTML-capable and display the HTML part of a multipart message. However, some mobile readers might be limited and display only the text part of the multipart MIME message. For this reason, it is important to always use a multipart MIME message instead of sending just a text or HTML message.