I'm glad to have found this thread, but its kept me up cleaning out thousands of "bounced" blocks from the last 2 day's suppression lists. They are both @gmail.com and gSuite/Workplace domains, and incidentally a ton of random blocks from Comcast as well from users that have months of open history.

This blew away about 10% of our newsletter and marketing subscribers. I can't imagine the time you're having if you send to millions of Google accounts.

Pardon me for being conspiratorial, but I have to say that the timing of these particular issues is of concern in light of the massive attacks the US government and others have faced this week. It seems adversaries would have plenty of fun if they got a new toy that could mess with the user/resource permission mapping at Google would want to use it to go after inboxes to do email confirmations. Even those this is 99% likely to be a DevOps chore that created an SRE nightmare, I'll allow myself believing 1% this was SecOps locking down huge swaths of accounts to mitigate a mass email verification attack.