Best posts made by Bizeren 0

Any email client that supports pop/imap should be able to connect to all of those mentioned websites and more. However it seems like you need to pay for protonmail's premium service and run their "bridge" app to use desktop email clients because of the encryption that protonmail uses - that could be why you have had issues in the past.
I personally use Thunderbird (free/open source) for several of the providers you've mentioned, but outlook (subscription) is also good especially if you also need exchange support.