There are three different writing styles for e-mail,but only two are common -- Neutral / Standard style and informal style.
The neutral/standard style is the style most commonly used in professional/work e-mail. because the writer and sender are busy,the language is simple, clear,and direct. Sentences are short,and there are use of contractions (I'm for I am,etc.). The language is personal,but the style is not similar ti speech-it is too direct