This is how you format an e-mailed query letter. Note that I did not begin with the recipient's address or my address or the date, as that is not customary for an e-mail. I also am not indenting because indenting and e-mails do not mix.
I am using block formatting. I double space between paragraphs but otherwise the query is single-spaced. It is written in a default font, it is left-justified, and the font is a normal size. If I have copied from a word processing program or past e-mail I am careful to make sure the fonts and sizes match. I haven't added pictures or tried to get fancy with anything because I want the agent to see that I'm confident in my words and don't need any gimmicks to make my query stand out.
Believe it or not, less than 25% of the e-queries I receive are properly formatted. While you won't get rejected if your query is incorrectly formatted, if you accomplish this simple task correctly you will convey an indispensable aura of professionalism. And remember: the amount of time you spend formatting, coloring, bolding, italicizing, and adding pictures to your query is inversely proportional to how professional it looks when you're finished.
Nathan Bransford (note that I didn't leave space for a signature since it's an e-mail)
My phone number
My e-mail address
(optional: my website/blog)
First 5 pages of the manuscript - don't worry about how these are formatted just do the best you can