Agreed on Mailspring, especially if OP wants a modern interface (although I think the new Thunderbird looks fine).
The only thing missing from Mailspring for me is seeing what folders my emails are in when I run a search. Otherwise, it’s the only non-CLI client I’ve found that let’s me use the keyboard to select multiple emails and move them to a folder, something I do in Gmail. If anyone knows of others, let me know! I’ve tried Claws, Evolution, Geary, KMail, and Thunderbird in addition to Mutt and aerc in hopes of finding something to replace Gmail…
derin