Even if the VPS is $5 a month it’s way more than using Migadu[1] which has a $19 plan with “unlimited” domains and aliases. Not even mentioning the burden of configuring, upgrading, and maintaining mailcow.
End to end encryption in email is a myth (unless you actually go through the process of encrypting your messages with a PGP key—that can be done with any provider), all ProtonMail does is encrypt your email on receipt.
Sorry, that's what I meant. With a VPS you're in control of the retention policy. With a managed provider you basically have no idea. Encrypting on receipt mitigates this.