sql_driver = mysql

[...]

mysql localhost {
  user = mailuser
  password = password
  dbname = mailserver
}

passdb sql {
  default_password_scheme = SHA512-CRYPT
  query = SELECT email as user, password FROM virtual_users WHERE email = '%{user}'
}

[...]

userdb static {
  fields {
    uid = vmail
    gid = vmail
    home = /var/mail/vhosts/%{user|domain}/%{user|username}
  }
}