nixpkgs/modules/programs/ssmtp.nix

# Configuration for `ssmtp', a trivial mail transfer agent that can
# replace sendmail/postfix on simple systems.  It delivers email
# directly to an SMTP server defined in its configuration file, wihout
# queueing mail locally.

{config, pkgs, ...}:

with pkgs.lib;

let

  options = {

    networking.defaultMailServer = {

      directDelivery = mkOption {
        default = false;
        example = true;
        description = "
          Use the trivial Mail Transfer Agent (MTA)
          <command>ssmtp</command> package to allow programs to send
          e-mail.  If you don't want to run a ``real'' MTA like
          <command>sendmail</command> or <command>postfix</command> on
          your machine, set this option to <literal>true</literal>, and
          set the option
          <option>networking.defaultMailServer.hostName</option> to the
          host name of your preferred mail server.
        ";
      };

      hostName = mkOption {
        example = "mail.example.org";
        description = "
          The host name of the default mail server to use to deliver
          e-mail.
        ";
      };

      domain = mkOption {
        default = "";
        example = "example.org";
        description = "
          The domain from which mail will appear to be sent.
        ";
      };

      useTLS = mkOption {
        default = false;
        example = true;
        description = "
          Whether TLS should be used to connect to the default mail
          server.
        ";
      };

      useSTARTTLS = mkOption {
        default = false;
        example = true;
        description = "
          Whether the STARTTLS should be used to connect to the default
          mail server.  (This is needed for TLS-capable mail servers
          running on the default SMTP port 25.)
        ";
      };

    };

  };

  cfg = config.networking.defaultMailServer;

in

mkIf cfg.directDelivery {
  require = [options];

  environment.etc =
    [ { source = pkgs.writeText "ssmtp.conf" ''
          MailHub=${cfg.hostName}
          FromLineOverride=YES
          ${if cfg.domain != "" then "rewriteDomain=${cfg.domain}" else ""}
          UseTLS=${if cfg.useTLS then "YES" else "NO"}
          UseSTARTTLS=${if cfg.useSTARTTLS then "YES" else "NO"}
          #Debug=YES
        '';
        target = "ssmtp/ssmtp.conf";
      }
    ];

  environment.systemPackages = [pkgs.ssmtp];
}