fphammerle/dovecot repository overview

docker run --name dovecot \
    -p ... \
    -v $PWD/dovecot.conf:/etc/dovecot/dovecot.conf:ro \
    fphammerle/dovecot

# dovecot.conf

auth_mechanisms = plain login

passdb {
  # https://wiki.dovecot.org/AuthDatabase/PasswdFile
  # doveadm pw -s BLF-CRYPT -u user -p password
  driver = passwd-file
  args = username_format=%n /etc/dovecot/passwd
}

service auth {
  # https://wiki.dovecot.org/Services#inet_listeners
  inet_listener auth {
    address = *
    port = 12345
  }
}

# postfix main.cf

smtpd_sasl_auth_enable = yes
smtpd_tls_auth_only = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = inet:dovecot:12345

smtpd_relay_restrictions = [...], permit_sasl_authenticated, reject_unauth_destination