A Google Groups thread is tracking a major problem for hundreds of Gmail users. Many users were noticing that their Gmail accounts were all of a sudden disabled.
Google has documentation on why an account would be disabled and what you would see if it happened to your account.
But this time it happened to way too many Gmail users for it to look normal.
The problem began late on December 5th. The following day, Gmail Guide replied saying that this was an error on Google's side and they are fixing it:
I understand that some of you have had a frustrating experience with your accounts being inappropriately disabled. Our team is aware of the problem, and our engineers are continuing to investigate. Thanks for bringing this to our attention.
Later that day, Gmail Guide posted that the issue has now been resolved. Any emails sent to a disabled Gmail account would have "received a bounce message informing the sender."
What was the issue, Gmail Guide said they misclassifed an abuse term which caused many Gmail accounts to be banned.
Then a bit later, Gmail Guide offered more explanation:
Our engineers work diligently to combat spammers who are attempting to abuse our system, and their work allows Gmail to function as an effective email solution to users everywhere. With this in mind, our engineers have built a monitoring system to minimize the impact that some of you ended up feeling.
The number of Gmail accounts this impacted was not released, but it seems it was more than just a few.
Forum discussion at Google Groups.