Formatted e-mail contains features that go beyond the limits of "Plain-Text" messages.

For comparison, plain-text e-mail would be any messages that
could have been prepared on a simple typewriter (for those who can
remember using such a device). In other words, you are limited to
a single font, or character style; you have only black ink; you
cannot include pictures or graphical symbols; and formatting is
accomplished by the simple use of spaces, tabs and carriage returns.

Formatted e-mail might include features like colored text; Special Fonts; font attributes like bolding, underlining and italicization; word-processing features like line justification, table and list formatting; inclusion of graphics, images and special symbols within the text; etc.

Most e-mail clients (like Thunderbird, Eudora, etc.) implement formatting by sending (and viewing) messages in the language of the world wide web: HTML. So, the same technology that you use to view web-pages is employed to give e-mail messages some visual flare.

E-mail clients that send formatted messages usually send these out in duplicate form: The first half of the message is sent in plain-text format; and the second half is sent in HTML.

Many people still use e-mail systems that only handle plain-text messages. If the message is not sent in plain-text format (along with the HTML part), many people will not be able to read it, or will find the actual message difficult to separate from all the formatting information.

One can send out a message that only includes the HTML half, but this would often be flagged as SPAM by the recipient's e-mail system. Frequently, spammers only send the HTML part, because they have something they want to show you, not because they have something they want you to read. This is particularily true of the most offensive SPAM.

Formatted e-mail has been used many times (and is still used) to send virus-laden e-mail messages. Because the e-mail client uses HTML to carry the formatting information, a "browsing engine" is used to display the message. Eudora, for example, uses the Internet Explorer browser to display formatted e-mail.

A web browser is a very common pathway for a computer attack. People are generally aware of the danger of "malicious web-sites", and stay away from browsing to disreputable sites. However, e-mail can and does come to you from all directions. It is impossible to completely control who sends you mail; and if your e-mail client is configured to display "previews" of your messages as they arrive, you can be taken off to some dangerous part of the web without even clicking on a link.

Every time a new vulnerability is published about Microsoft's Internet Explorer browser, there is a flurry of new e-mail sent out by spammers that includes the exploit in the formatting.

There are many things one can do. Here at the Waisman Center, we have policies that discourage the use of HTML in e-mail messages; and we have always recommended use of less vulnerable browsers like Netscape, Mozilla, and Firefox.

In the new Thunderbird e-mail configuration, we have disabled HTML as the default mode for composing messages.

Also, for viewing e-mail messages, Thunderbird is configured to display "Simple HTML". This only permits the most basic forms of formatting that are not passed on to a full web browsing display engine. You can set your e-mail client to view "Plain Text" for even more assurance; or to "Original HTML" if you trust that incoming messages will not be harmful. These options are discussed below.

Even though our configuration of Thunderbird enforces plain-text for composition of outgoing messages, you can still choose to use the formatting toolbar for individual messages.

If you hold down the [Shift] key when you click the "Write", "Reply" or "Reply All" toolbar buttons, the compose window will open with the formatting toolbar displayed.

You should only do this when you know that all recipients are capable of reading formatted messages.

If you have received a message that you think has more than simple formatting and you trust it to be safe, you can use Thunderbird's full HTML viewing mode by clicking "View", "Message Body As>", "Original HTML".

Note that this will change your viewing mode for the remainder of your session, until you change it back (to Simple HTML). Unsolicited e-mails could catch you off guard in this mode.