SOLVED How to save (so as to share later) a complex Mac Mail mailbox (OS 10.14 Mojave)

[AutoMac]

I have managed the daily running and maintenance of a block of 15 apartments for the past 5 years. All correspondence with apartment owners and suppliers is channeled through my iMac's Mail app. Over this period this single top-level mailbox now has multiple (40+) sub-mailboxes each containing correspondence on a specific topic.

At some stage in the future I expect to want to hand over my duties to another person and I am trying to find a way in which I can copy the entire top-level mailbox complete with all it's sub-mailboxes (and thousands of emails) in one single back-up file that I can then pass all this entire history to the next person (who may be a Mac or PC user - to further complicate the issue). I absolutely want to avoid having to print or copy each individual sub-mailbox...

I run the usual Time Machine back-ups all the time, but this type of back-up does not appear to be remotely suitable for the purpose of sharing the mailboxes in the future. Would any learned member of this forum have any helpful suggestions please?

 

[Lufbrarunner]

Could you 'Export' the mailboxes, and then 'import' them to the new users system?

 

[AutoMac]

Hi Lufbrarunner, thanks for that thought. "Yes" I expect that I certainly could if that was going to produce the one complete file to share. If that is the best route it may raise a question of the best format to do the export (if there is a choice) for the easiest way to share on multi OS machines (Mac or PC).