MUA-facing IMAP and SMTP (submission) proxy with Dovecot

Forwards IMAP and SMTP (submission) connections from MUAs to different backend servers based on the mail domain.

dovecot_proxy:
  domain_proxies:
    example.com:
      backend_host: myoldmailsetup.net
    mymaildomain.org:
      backend_host: mynewmailsetup.org

This proxies users with @example.com email addresses to myoldmailsetup.net and users with @mymaildomain.org email addresses to mynewmailsetup.org.

Make sure to setup ssl certificates (see defaults for ssl_cert and ssl_key).