{...}: {
  environment.persistence."/srv".directories = [
    {
      directory = "/var/lib/mail/backup";
      user = "virtualMail";
      group = "virtualMail";
      mode = "0700";
    }
    {
      directory = "/var/lib/mail/sieve";
      user = "virtualMail";
      group = "virtualMail";
      mode = "0700";
    }
    {
      directory = "/var/lib/mail/vmail";
      user = "virtualMail";
      group = "virtualMail";
      mode = "0700";
    }
    {
      directory = "/var/lib/mail/dkim";
      user = "opendkim";
      group = "opendkim";
      mode = "0700";
    }
  ];
}