Because email is so quick to SEND it is very important to read it over and proof it.
I make the most errors in email when I go back and change a sentence, add something, take something out and if I am not careful it goes out with errors: The sentence structure is wrong. The tense is not right. It doesn't make sense anymore!
If you have gone back and made changes to an email, read it over once again before pressing SEND to make sure it still says what you want it to say.