You can host a Proton mail bridge to use different apps running on different machines, including phones.

Self hosting e-mail, particularly SMTP, will likely require a static IP from a reputable provider. Mail servers may reject incoming mail based on the reputation of the sending server. You can avoid this by relaying through another SMTP server and configuring your DNS rules to allow that server to send mail on your behalf, but that’s not really self hosting anymore.

This is a states’ rights issue: the right of the state to do what is convenient for the states’ rights party.