Emails as evidence in court

Hi:

I’d like to know what are the different ways to use email as evidence in court.

Specifically, I’d like to know what happens in the case of emails that are no longer in the inbox or stored in a folder in the Mac, using Mail, but are still available through the sent folder with it’s original message, its reply, and several other replies there. Because this is the sent folder, you can’t see the headers so the question is what are other ways to use them as proof. I know this is may be different according to local law, although it would be good to know what’s technically possible or from the point of view of legal common sense.

Thanks in advance.