I'm likely woefully uninformed on this, so I'd like to ask for some information. Last I heard/looked (many years ago), Proton was just webmail-only, I think. Can it actually do all the same things Fastmail can, as in IMAP/SMTP access, catch-all addressing (*@mydomain.tld routes to realaddr@mydomain.tld; I'm the only user and own the entire domain, allowing me to do stuff like linkedin@my.tld, pizzahut@my.tld, apple@my.tld and so on; so I know who's up to shady sh!t), MX records for a custom domain, built-in spam filtering, custom user-editable rules, 2fa, per-app passwords, and so on?
Because if it's got close to 1:1 feature parity (or better) I might consider a switch once my existing paid plan is up.