This morning users on the Shadow server briefly saw the message "Your recipient address has been blocked by admins" when sending emails to any recipient @gmail.com. It is difficult to say precisely what caused this, but we can attribute the result to our automation. It was resolved relatively quickly, but not without users seeing the problem first.
We have seen an unusual increase in users on our service sending emails to invalid recipient domains. We realize that you cannot always prevent this, so we are taking steps to reduce the volume of it on our side. This means we are parsing logs for invalid recipient domains, adding them to a list, and preventing emails from even attempting to send to those domains later. Unfortunately, gmail.com was caught in one of these automated sweeps. The actual logic for how and why it ended up there is what is presently unknown, as the simple answer is mitigated by the fact that this only occurred on the Shadow server (while the same DNS service used to experience the temporary failure is shared across every server).
The automation is dead, it won't be coming back unless and until we add failsafes.
