In Windows, how do I force my email client to display mail as text-only?

By default, most mail clients will fully display HTML messages. Outlook will prompt you before downloading images, but some of the HTML formatting, as well as other code, can still execute.

The problem with allowing HTML or any other non-text-only formatting when viewing email is that malicious mail senders (spammers, Trojan writers, etc.) can write code that will make your mail client do something that you otherwise would not allow. For example, spammers can verify that their spam message is read by including a 1-pixel image in their HTML-formatted pages. It is so small that you don't even see the image when you read the spam. But when you open the message, the email client will see and execute the HTML code calling for the 1-pixel image to be downloaded. Since executing the HTML involves contacting the server hosting the image, the spammer will now know that the spam was actually read, and most likely by a real human since most automatic readers (such as spam filtering programs) will not execute the code calling for the image.

Other problems with allowing anything other than text-only in your mail client is that viruses, worms, and Trojans can take advantage of the mail client's ability to execute code in order to infect your computer. The best security practice is to set your email client to read mail as text only.

To force text-only viewing of messages in your mail client:

Outlook 2003

1. From the Tools menu, select Options... .
   
   
2. Click E-mail Options... .
   
   
3. Check Read all standard mail in plain text.

   There is also a setting labeled Read all digitally signed mail in plain text. Normally, digitally signed mail is from a sender you know, or at least a responsible mail sender in your organization, so in most cases it's safe to read such mail in whatever formatting it was sent.

4. Click OK twice.

Outlook Express

1. From the Tools menu, select Options... .
   
   
2. Click the Read tab.
   
   
3. Check Read all messages in plain text.
   
   
4. Click OK.

Mozilla Thunderbird

From the View menu, select Message Body As, and then select Plain Text.

Eudora 6.2 or later

You cannot completely disable HTML rendering of incoming messages in Eudora. Some code will still execute; for example, links will still appear as underlined text just like in a web page, rather than URLs in brackets. However, you can use settings that minimize the level of this execution, as follows:

1. From the Tools menu, select Options.
   
   
2. Under "Category:", select Display.
   
   
3. Uncheck Automatically download HTML graphics and Show attachment images inline.
   
   
4. Under "Category:", select Viewing Mail.
   
   
5. On the right under "Message Window", uncheck Use Microsoft's viewer. Then, near the bottom of the Window, uncheck Allow executables in HTML content.
   
   
6. If you also want to disable the sending of HTML formatted messages, then under "Category:" select Styled Text. On the right under "When sending mail with styled text (HTML):", select Send plain text only.
   
   
7. Click OK.

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