{
  flake,
  config,
  lib,
  pkgs,
  ...
}:
{
  networking.firewall.allowedTCPPorts = [25];

  services.postfix = {
    enable = true;
    relayDomains = ["hash:/var/lib/mailman/data/postfix_domains"];
    # get TLS certs for list.pub.solar from acme
    sslCert = "/var/lib/acme/list.pub.solar/fullchain.pem";
    sslKey = "/var/lib/acme/list.pub.solar/key.pem";
    config = {
      transport_maps = ["hash:/var/lib/mailman/data/postfix_lmtp"];
      local_recipient_maps = ["hash:/var/lib/mailman/data/postfix_lmtp"];
    };
    rootAlias = "admins@pub.solar";
    postmasterAlias = "admins@pub.solar";
    hostname = "list.pub.solar";
  };

  systemd.paths.watcher-acme-ssl-file = {
    description = "Watches for changes in acme's TLS cert file (after renewals) to reload postfix";
    documentation = ["systemd.path(5)"];
    partOf = ["postfix-reload.service"];
    pathConfig = {
      PathChanged = "/var/lib/acme/list.pub.solar/fullchain.pem";
      Unit = "postfix-reload.service";
    };
    wantedBy = ["multi-user.target"];
  };

  systemd.services."postfix-reload" = {
    description = "Reloads postfix config, e.g. after TLS certs change, notified by watcher-acme-ssl-file.path";
    documentation = ["systemd.path(5)"];
    requires = ["postfix.service"];
    after = ["postfix.service"];
    startLimitIntervalSec = 10;
    startLimitBurst = 5;
    serviceConfig.Type = "oneshot";
    script = ''
      ${pkgs.systemd}/bin/systemctl reload postfix
    '';
    wantedBy = ["multi-user.target"];
  };

  services.mailman = {
    enable = true;
    serve.enable = true;
    hyperkitty.enable = true;
    webHosts = ["list.pub.solar"];
    siteOwner = "admins@pub.solar";
  };

  # TODO add django-keycloak as auth provider
  # https://django-keycloak.readthedocs.io/en/latest/
  ## Extend settings.py directly since this can't be done via JSON
  ## settings (services.mailman.webSettings)
  #environment.etc."mailman3/settings.py".text = ''
  #  INSTALLED_APPS.extend([
  #    "allauth.socialaccount.providers.github",
  #    "allauth.socialaccount.providers.gitlab"
  #  ])
  #'';
}