Tap out of Developer Beta - restore previous MacOS

I've previously tapped into the developer program and currently running macOS 10.12.1 (16B2553a) (like to be first mover on software 🙂 )

- However for various reasons I would like to go back to the latest public release of MacOS - but I' would very much like that all my emails (mailboxes) and accounts are saved first to external media - before I restore my iMac.

Is there a "how-to" or "step-by-step" out there that show the best and easiest way for doing that?