Migration from VERY old Ubuntu 12.04/Zimbra 8.0.7 to Ubuntu 18.04/Zimbra 8.8.15

As you can tell from the title I have been using Zimbra and Zextra a long time. I currently am using Zextra 2.14 and have already re-licensed Zextra 3.0.5.

This is a personal email server with less than 10 boxes and all I want to do is move email, contacts, calendars and aliases. The email isn't as important as the other stuff. Seems pretty straight-forward. The fact is this machine has been running so smoothly for over 8 years and now I am behind the 8-ball.

There must be some simple steps to get this done.

Any help will be greatly appreciated of course and I apologize since I am sure this is redundant. I document well so I will be glad to create a STEP-BY-STEP document.

Thanks.