I was under the impression Proton Bridge was available for any paid subscription. I've had a Visionary plan for years, so I can't say for certain since I get a lot of perks as a result.

The bridge is a bit tetchy, sometimes it works, sometimes it don't, and can never really say why. You also need to have the bridge app installed on the machine you're using it on (eg won't work on mobile or any unsupported platform). The tl;dr for this is if you need to rely on SMTP / IMAP ProtonMail isn't ideal.

I do actually have Proton Bridge running on my Yunohost machine, the CLI version was annoying to set up but that is the only install I haven't had too much issue with (yet). The thing to be aware with that Proton is super anal about the email address you're sending from, if it isn't an alias (or a hosted domain) on the account it isn't going to have any of that.

In terms of self-hosting though, I have a Wildduck install running. The software isn't really production ready, but for a personal home server does the job super well. You can also get it to auto-encrypt incoming emails with PGP (similar to Proton) and it saves emails you send via SMTP to your Sent item folder automatically.

My advice for self-hosting though, is use a SMTP Smarthost from a professional provider (I've always used Duocircle and Spamhero), Google and Microsoft make self-hosting a nightmare even if you are fully compliant, but these operators give you a better chance of getting through.

Because I'm lazy, I also use MXGuardDog to filter incoming email, I rack up free credits by placing a link on my website so I've never once paid for the service in cold hard cash. But realistically you could skip this part.