Proton mail doesn't support IMAP, 3rd party clients, or email export. If you decide you no longer want to use Proton but you want to keep some of your emails, you have to manually save the contents of each message. It's irresponsible to recommend Proton without mention of the commitment involved.

Oh yeah - lol - email clients. I remember them. No, the solution has to work seamlessly with gmail, yahoo, hotmail, outlook, whatever clients people are using. It needs to be everywhere or it might as well require a different protocol/client altogether.