AOL took down its mail servers to do a hardware upgrade between 1 a.m. and 3 a.m. PT. But problems kept it offline until 5 a.m. PT.
AOL officials estimated that the outage directly affected about 20,000 people who tried to send or receive mail during the outage, spokeswoman Tricia Primrose said. Last week's outage affected 150,000 of AOL's 8 million-plus subscribers.
But many others experienced delays all day because of the brief outage. While the system is down, AOL continues collecting the mail but doesn't resume delivery until it comes back up.
Because so many pieces of email flow through AOL's system every day--some 14 million, according to senior vice president David Gang--even a brief outage can cause a major traffic jam. Traffic generally takes several hours to clear, Gang said, likening the backup to an airport suffering flight delays because of bad weather.
Because the online service is so large, AOL's email problems are often felt by other ISPs. For instance, when AOL had its major outage last August (the system crashed for 19 hours) several Internet service providers saw their systems clog up with bounced email from the AOL system.
In this case, however, AOL's mail servers continued to accept mail. That did not comfort all members, many of whom rely on AOL for business.
"AOL's demonstrated a long-standing insensitivity to reliable mail delivery," said critic David Cassel, who publishes the AOL List. "What makes this more galling to AOL's users is the fact that AOL has resumed its marketing efforts to expand the service. They can't even service their current subscriber base."
But Gang said email generally is good and defended the company, saying AOL is doing everything it can to keep up with demand. Last year at this time, members were sending and receiving about 4 million pieces of email a day, less than a third less than they are now.
"The number of emails passing back and forth has skyrocketed," Gang said. "It's going to take some time for the overall situation to catch up."