depot/third_party/nixpkgs/nixos/tests/postfix-raise-smtpd-tls-security-level.nix

import ./make-test-python.nix {
  name = "postfix";

  nodes.machine =
    { pkgs, ... }:
    {
      imports = [ common/user-account.nix ];
      services.postfix = {
        enable = true;
        enableSubmissions = true;
        submissionsOptions = {
          smtpd_tls_security_level = "none";
        };
      };

      environment.systemPackages =
        let
          checkConfig = pkgs.writeScriptBin "check-config" ''
            #!${pkgs.python3.interpreter}
            import sys

            state = 1
            success = False

            with open("/etc/postfix/master.cf") as masterCf:
              for line in masterCf:
                if state == 1 and line.startswith("submissions"):
                  state = 2
                elif state == 2 and line.startswith(" ") and "smtpd_tls_security_level=encrypt" in line:
                  success = True
                elif state == 2 and not line.startswith(" "):
                  state == 3
            if not success:
              sys.exit(1)
          '';

        in
        [ checkConfig ];
    };

  testScript = ''
    machine.wait_for_unit("postfix.service")
    machine.succeed("check-config")
  '';
}