Protonmail suck. Avoid them.
Protonmail are a terrible email provider and I would advise that you avoid their services. Protonmail do not let you access your emails in a 3rd-party client without their bridge application. If you want to move to another email service, they do not offer forwarding for old emails. Protonmail do not support SMTP/IMAP. They claim they do. This is a lie, because everything has to go via bridge. And you have to pay for bridge. They filter legitimate emails as spam and block emails from some legitimate domains entirely.
If you're on a free account, they do not let you have more than one filter. This wouldn't be an issue except that you can't use any client other than their webmail on a free plan.
Also, their webmail is slow, ugly, and bloated beyond belief with JS. Just don't.
What do I use instead?
rn I'm trying out Migadu for my email. More on them in the future, if they're much better. See also Drew Devault's page on email providers. Avoid any free email service. Free email is never really free.Migadu
Drew Devault: email providers
Also to avoid: Any megacorp (gmail, hotmail, outlook)