> I find IP based mail blacklist services such as BRBL obsolete and possibly harmful. Now that we have domain verification services like DKIM SPF etc. Blacklist the domain.

SPF and DKIM require opt-in by the sending domain, of which the majority of non-commercial non-US outgoing MTAs do not do. IP-based blocklists, including Spamhaus PSBL Mailspike etc, are all valuable to catch IP addresses that should not be directly connecting to your MTA. I agree that signing up for an outgoing MTA service such as Sendgrid makes some IP-based checks obsolete but that's not where the majority of spam is coming from. Botnets continue to be the number one source of junk email and will likely continue as we add more and more insecure doorbells, garage openers, refrigerators, etc, to our home networks.