It depends on who I'm sending them to, if I'm sending one to a close friend or my boyfriend they tend to be several paragraphs long at least.
If it's just an acquaintance though I don't write more than one paragraph most of the time.

For the most part they are usually short,,sometime only a couple of sentences.

Depends on who I am writing, and when we were last in communication. If it has been a while, or if there is a lot to say, then it is longer than if I talked to the person 30 minutes ago. My SO and I have a rule that emails must be a minimum of 100 words long, or else it does not get a response.

Depends on the purpose of the email and who it's too. I would say that generally, I am short and to the point. If it's to someone that is a lover or a friend, I may write longer. I do not talk a lot usually, so my letters and emails are usually shorter.

If I havent talked to some one in a long time I send out some long ones but they are not always long.