This article explains how to create an alternative to bold in a plain text email using plain text characters. You can make your words stand out and mimic bold text, even if the message format constraints don't support it.

The best bold alternative to plain text is to use asterisks. Surround the text you want to emphasize with asterisks to make it stand out from the rest of the words. Examples include:

This approach is only effective if you limit the boldface trick to a small group of words. The ideal number of words to put within the asterisks is one to four. If you use more, readers may forget that the first asterisk exists until they see the second. In other words, putting an asterisk at the beginning and end of a 500-word email doesn’t make the text stand out.

Another option is to use hyphens or double hyphens to separate a few words and draw attention to the text. They are not as common as asterisks for making text bold, but there are no hard and fast rules here. The only purpose is to make text look bold in any way.