Honestly, get a small VM at openbsd.amsterdam or another good hoster and just do it yourself. OpenBSD has outstanding documentation, standing up SMTPD and Dovecot there is super simple, especially for a single user and not a whole group or family (where LDAP or Kerberos would be warranted). Just take initiative and own your data. Does it cost a little bit upfront time? Sure, but maybe just weekend. Does it require a little maintenance here and there? Sure. But still cheaper than paying for fastmail or waiting for fastmail to also exploit your data because the shareholders said so....just own your data.