I really need an e-mail client, so I just downloaded Sylpheed. Upon starting it up, the first thing it asks me is where I want my mailbox to be.
I never thought about this before. But, now that I think about it, this was one of the reasons I found Thunderbird annoying to use many years ago. I took its operation for granted, but it just stored my mail someplace deep in my personal folders, and it was annoying to figure out how to move it to another computer. I eventually didn't even bother.
The fact that Sylpheed is asking me is a good sign.
I also tried Sylpheed years ago but for some reason it was slow. Both it and Thunderbird were. Dunno why. Hopefully things are better this time.
Oh, also, #Sylpheed is #OpenSource and #FOSS. I need to use the beta in order to get OAuth2 though, I think. So I'll find out later how well this works.