What to do before I wipe my old Mac

My new iMac has been up and running for a few months so I'm ready to wipe my old iMac. I've deauthorized iTunes on the old one and signed out of my Dropbox account. The old one didn't have iCloud set up, so I think I'm good there. Should I do anything with Mail? If I delete all my emails on the old Mac will they still be there on the new one? They're backed up but I would hate to be surprised when I turn my new one back on. Is there anything else I should do before wiping?

Thanks