Are you emailing your query letters to prospective agents and publishers? If so, I hope you are using the same etiquette you would use for snail mail. That means you begin your letter with Dear Ms. or Dear Mr. Agent. Then you write out your three or four paragraphs using proper spelling and grammar without any text or email shorthand (lol, 4 instead of for, u for you, etc.).The only real format difference is that instead of having your contact information in the letterhead, you can include this info under your signature.
Make sure you follow the submissions guidelines as far as attaching copy or including your writing sample in the body of the email. And don't forget to check and double check the spelling of the agent's or editor's name.
My new ebook, Four Ps to Publishing Success, has a whole chapter dedicated to making yourself attractive to agents and editors. You'll find guidelines on how to prepare a professional letter and eight tips for crafting an irresistible query. Check it out!