On the 2024-01-07 a spammer made a large flow on one of the external submission servers. The server stopped the spam mails, and saved them to a separate holding queue to make room for other users.
It took a while for the reporting to get to the operations team, but as soon as the issue was known it was swiftly resolved at ~19:00. However, meanwhile the server ran out of space, and some users (who hit that server) would have seen that the send and receive activities failed.
We apologize for the inconvenience that this issue has caused, and will focus on improving the reporting to also cover this specific issue.