Yesterday, AOL fell because of a “software bug” that prohibited any email to be sent or received by the millions of subscribers to the giant ISP. After an unspecified time (visibly less than 24 hours), the operation could be restored.
It seems that there was no email lost. The very old but robust email protocols and the huge equipment of AOL allowed the queuing of received and sent messages. So it was only a delay for the messages of most users. They are churning 500,000 messages per minute to correct the situation.