mailutils depends on OpenSSL 1.0.2, which is marked as insecure and thus prevents this package from being built on Hydra. Excluding it by default should re-enable binary builds for users who don't need the email feature. This change is unlikely to cause a major disruption because there's an existing NixOS module for smartd that handles email notifications. It works without this package being dependant on mailutils. Since mailutils isn't used for any other purpose besides providing email notification for smartd, it's possible to drop it without feature loss. This change also makes the dependance on inetutils optional. inetutils is needed for the 'hostname' command, and is only used for providing email support.