Have happily used PMAIL since around 1985, but due to issues beyond my control I may have to convert to Thunderbird.

I have ~30K messages, organized into lots of subject specific folders. I would (obviously) like to maintain that same organization.

Are there best practices to follow in doing this?

All advice and cautions are welcome.

(Context: have been a (mostly) Windows and (also) Linux user for since 1985, so suspect I can do most things required, if only I knew what to do. Have had enough experience to know that there can be numerous gotcha's, and doing it right the first time is infinitely easier than trying to slog through it, hence the request for guidance.)

many thanks
Randy