I'm with you about not inviting MacMail's wrath . . . I wrestle with it, it usually wins.
But . . . in the past I had success using Chronosync to synch up Mail's folders between my iMac and my MBP. I probably had an easier situation that you do, because I only bothered doing it when when I was going to travel. I rarely used Mail on the MBP when not traveling.
But it did work. As I remember, I used the option of making the two match (synching by going back and forth) rather than just copying from the iMac.
I also remember that occasionally the whole process crashed and burned, although it wasn't Chronosync's fault.
And, I have a 'history' with some of Apple's apps. I crashed iTunes some six years ago now so hard, it deleted corrupted the database, and deleted tracks, and I had to, under the direction of a 'second level engineer' at Apple, reloaded all of my physical CDs. iTunes crashed on me several times, but that was the worst. Heck, once iTunes would not import a CD, no matter what I did. Couldn't figure that one out at all...
I poke macOS mail as little as possible. Seeing the rules are in a single XML file, and finding another XML file with a list of the rules is a little ominous. I can see the reason for them being in a single file, but having the separate list of rules makes me wonder what other surprises there could be if I try to 'fix' the Apple Mail hot mess. Like, is that list automagically maintained? If I add a new rule 'behind the curtain', will it invoke the wrath, or will Mail just add it to the list, or flush it from the file, or just ignore it. It seems embarrassing, and somewhat distressing, to have to wonder about such questions, and fear the wrath of that app. So fragile is the system we depend on for our contact to the 'real world'.
I only have three systems that I usually have on and collect email, but the thought of having to pull each of those files up on one system and edit them to add the missing rules, and annotate them in the list, and gross my fingers, toes, and eyes as the systems come up is something that I don't know I can survive. If Mail goes all wrath, I may just quit.
I do remember editing an XML file that likely caused the massive iTunes crash. I was amazed that it appeared that iTunes *knew* I tried to move the cheese manually... How did it know? The Apple 'engineer' didn't know. Just freaky...
I could go from system to system and create the rules on each one, but some systems have 25 to 30 rules. (I found out that when Mail had a small number of massive rules, it took much longer than having multiple smaller rules, which was surprising too, and more odd since all the rules are essentially in the same XML file. It takes them that much to scan the entries in the key blocks, than scan multiple key blocks) Odd... Strange even...
AND Mail rules sometimes flip to the previously entered actions and folder names, just at random. Maddening...
Yeah you don't tug on superman's cape
You don't spit into the wind
You don't pull the mask off the old lone ranger
And you don't mess around with Apple XML files?
