> The real culprit is the domain registrar and the DNS server software. Neither of those should be enabling invalid domains to be accessible. They already don'

> The real culprit is the domain registrar and the DNS server software. Neither of those should be enabling invalid domains to be accessible. They already don't. DNS does not forbid underscores, and places hardly any restrictions on labels. Hostnames do forbid underscores, and that muddies the water quite a bit. While disallowing A-records on labels with undersores would make sense, a CNAME on a label with an underscore can point to a domain without one, and the one it points to may or may not have an A-record. It is really up to the client to decide that a domain name is invalid for their use case, but clients don't want to disallow something that appears to otherwise work fine. And so we end up in a situation where none of the specifications are truly followed.