Whilst I agree people should at least have a ".com" backup domain (at least for email use), many services are supporting the less common TLDs nowadays. In particular, ".dev" seems to be supported well in my experience (where Experian has been the only problematic service).

As for the spam filters, whilst the domain definitely does play a part in some cases - there's more to it than that. Having the correct security configuration (DKIM, etc.) and a "trusted" mail server (good luck asking M$ for their list, though) goes a long way.