On one machine I have offlineimap.py[1] (with mutt), on the other laptop Evolution[2] that archives my mail locally that I can also export and back up regularly.
Do you have anything set up with evolution to handle things automatically?
Re offlineimap, just looked into isync/mbsync suggested here by others, it seems better from the description, I'm probably going to try it when I have some time: https://people.kernel.org/mcgrof/replacing-offlineimap-with-...