Emails are used as evidence the same way any other written communication, such as a letter, is used. You can print it out but be prepared to be asked a lot of questions about how you got it. Be sure not to delete the original version that is in your inbox. It is best if you can print the email out with all its "header" information. Very few cases involve faked emails. Judges realize that not too many people are sophisticated enough to fake an email convincingly, and that they almost always have far more to lose by trying to introduce fraudulent evidence than they could gain by fooling anyone.