I hate Google as much as the next fedizen but I think this one might just not have a catch. It’s nothing crazy, just that if you’re sending more than 5000 bulk emails/day to gmail users, you have to set up proper DNS records, which if you’re managing a private email server you should probably have done anyways.

SPF, DKIM, and DMARC are standards that improve email sender authenticity and should be enforced by every email provider. This is a great next step that basically enforces that the source of the message is pre approved by the domain’s owner. There’s no downside and any company seriously impacted isn’t using bare minimum email sending settings.
You still have to be cautious for lookalike domains, but this should help block lazy spoofing attempts.

The catch is if you wanna spam Gmail accounts you’ll need to register with Google and most likely pay a fee to bypass the filter.

Yahoo did it too and might have actually been competition to gmail.

Google have to pay for the storage of that spam emails in Gmail users inboxes, not paying for that storage is the catch.

You have to send something like 5000 emails a day. They’re fine