[Systemmanic]

Looks as though this Comcast “security feature” can be disabled via your account settings.

Also, DNSSec?

[vladvasiliu]

I'm not an expert on DNS, but I don't think DNSSec can actually help here, and by help I mean "unblock".

Sure, their NXDOMAIN (or whatever) response will appear bogus, but your client won't be able to rebuild the missing response.