Thanks all for your comments - much appreciated.
Whether or not I use a home partition, the important thing for me was to be able to export/import individual email folders + contents for archiving purposes on backup media. Particularly important since the email box I'll be using seems only to have POP, which surprised me. I've discovered by playing with Evolution and Claws that I can do this very easily by means of something called an mbox file (this is all new to me!). Interestingly, I find that Claws has the edge with usability for this aspect.
If Thunderbird has the ability to export/import mbox files in its menus, I have yet to find it, so I'm kicking Thunderbird into touch straight away. I've found the mbox files for both Evolution and Thunderbird deep within the labyrinth of their hidden folders and I can import these (with difficulty) into Thunderbird and with consummate ease into Evolution and Claws, so another reason not to use Thunderbird. But I'll be using the import/export menu items anyway.
Next step is to set up both Evolution and Claws for day-to-day use. Since it's so easy to export from one and import into the other I can use one for a week, transfer all my emails and use the other for a week and so on, and can take my time deciding which is better for me while still keeping all my emails together.
Thanks so much. It's being not confident that there's an easy import/export that's held me back before.