Millions of AOL users encountered delays sending and receiving e-mail Thursday as the company worked to identify and fix a software glitch.

AOL spokesman Nicholas Graham said the company was investigating the cause of the problems, which began late in the morning.

He said millions of messages were stuck in a queue and all would eventually get delivered. But as technicians tried to fix the problem, he said, users faced difficulties accessing their accounts, particularly through AOL's Web interfaces.

The glitch affected both AOL.com e-mail for paid subscribers and its free AIM.com offering.

As of March 31, AOL had 18.6 million subscribers in the United States. According to comScore Media Metrix, AOL had 43 million active users of its AIM instant-messaging service in April, all of whom are eligible for AIM.com e-mail accounts.