nixos/services/nginx_vHosts/mail.nix

{
  config,
  lib,
  ...
}:
with lib;
{
  vHost =
    if config.mailserver.enable then
      {
        serverName = config.mailserver.fqdn;
        enableACME = true;
        forceSSL = true;
      }
    else
      { };
}
.vHost