The Body
The body of an email contains raw text. This text, even when formatted, is actually just raw ASCII text until it is received by a client and any specific formatting in HTML is translated and applied.
There are certain advantages to using HTML formatting in an email. The first is that many users feel the aesthetics of a fully formatted email are more appealing. Additionally, metadata, inline links, and hypertext can augment the informative and data-based value of an email. Emphasis is also made easier and more standard with traditional formatting such as underlining and italicizing. Formatting in plain text follows different conventions that are accepted, but not necessarily universally known or standardized.
HTML formatting does come with a few disadvantages as well, including a significant increase in the email size and the potential for incompatibility with older email clients. The most significant drawback of an HTML-formatted email is the potential for security breaches which may occur if HTML code is intentionally inserted with the express purpose of introducing a Trojan Horse.
