nixos/applications/email.nix

{ config, pkgs, lib, ...}: with lib;
  let
    cfg = config.services.skynet_email;

    # create teh new strings
    create_filter_array = map (x: "(memberOf=cn=${x},ou=groups,${cfg.ldap.base})");

    create_filter_join = (x: concatStringsSep "" x);

    # thought you could escape racket?
    create_filter = (groups: create_filter_join (create_filter_array groups) );

  in {

  imports = [
    ./dns.nix
  ];

  /*
  backups = [
    "/var/vmail"
    "/var/dkim"
  ];
  */

  options.services.skynet_email = {
    # options that need to be passed in to make this work

    enable = mkEnableOption "Skynet Email";

    host = {
      ip = mkOption {
        type = types.str;
      };

      name = mkOption {
        type = types.str;
      };
    };

    domain = mkOption {
      type = types.str;
      default = "skynet.ie";
      description = lib.mdDoc "domaino";
    };

    sub = mkOption {
      type = types.str;
      default = "mail";
      description = lib.mdDoc "mailserver subdomain";
    };

    groups = mkOption {
      type = types.listOf types.str;
      default = [
        # general skynet users
        "skynet-users"
        # C&S folsk get access
        "skynet-cns"
        # skynet service accounts
        "skynet-service"
      ];
      description = lib.mdDoc "Groups we want to allow access to the email";
    };

    ldap = {
      hosts = mkOption {
        type = types.listOf types.str;
        default = [
          "ldaps://sso.skynet.ie"
        ];
        description = lib.mdDoc "ldap domains";
      };

      base = mkOption {
        type = types.str;
        default = "dc=skynet,dc=ie";
        description = lib.mdDoc "where to find users";
      };

      searchBase = mkOption {
        type = types.str;
        default = "ou=users,${cfg.ldap.base}";
        description = lib.mdDoc "where to find users";
      };

      bind_dn = mkOption {
        type = types.str;
        default = "cn=admin,${cfg.ldap.base}";
        description = lib.mdDoc "where to find users";
      };

    };
  };

  config = mkIf cfg.enable {

    age.secrets.ldap_pw.file = ../secrets/ldap/pw.age;

    # set up dns record for it
    skynet_dns.records.external = [
      # basic one
      "mail A ${cfg.host.ip}"

       # SPF record
      ''${cfg.domain}.                 IN TXT "v=spf1 a:${cfg.sub}.${cfg.domain} -all"''

      # DKIM
      ''mail._domainkey.${cfg.domain}. IN TXT "v=DKIM1; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDl8ptSASx37t5sfmU2d2Y6yi9AVrsNFBZDmJ2uaLa4NuvAjxGQCw4wx+1Jui/HOuKYLpntLsjN851wgPR+3i51g4OblqBDvcHn9NYgWRZfHj9AASANQjdsaAbkXuyKuO46hZqeWlpESAcD6a4Evam4fkm+kiZC0+rccb4cWgsuLwIDAQAB"''

      # DMARC
      ''_dmarc.${cfg.domain}.          IN TXT "v=DMARC1; p=none"''
    ];

    skynet_dns.records.reverse = [
      "${builtins.substring 9 3 cfg.host.ip} IN PTR ${cfg.sub}.${cfg.domain}."
    ];

    mailserver = {
      enable = true;
      fqdn = "${cfg.sub}.${cfg.domain}";
      domains = [
        cfg.domain
      ];

      # 20MB max size
      messageSizeLimit = 20000000;

      ldap = {
        enable = true;
        uris = cfg.ldap.hosts;
        bind = {
          dn = cfg.ldap.bind_dn;
          passwordFile = config.age.secrets.ldap_pw.path;
        };

        searchBase = cfg.ldap.searchBase;
        searchScope = "sub";

        dovecot = {
          userFilter = "(skMail=%u)";

          # accept emails in, but only allow access to paid up members
          passFilter  = "(&(|${create_filter cfg.groups})(skMail=%u))";
        };

        postfix = {
          filter = "(skMail=%s)";
          uidAttribute = "skMail";
          mailAttribute = "skMail";
        };

      };

      # feckin spammers
      rejectRecipients = [

      ];

    };

    # tune the spam filter
    /*
    services.rspamd.extraConfig = ''
      actions {
        reject = null; # Disable rejects, default is 15
        add_header = 7; # Add header when reaching this score
        greylist = 4; # Apply greylisting when reaching this score
      }
    '';
    */
  };
}