A Microsoft spokeswoman said the company first discovered the problem at 6:30 a.m. Pacific time and "fully restored" service by 9:50 a.m. The spokeswoman said no customer data was lost during the outage. She declined to offer further details about the nature of the problem.
During the outage, attempts to log in were met with a message, saying: "This server is too busy." Since the Hotmail home page did appear, the company had advised customers to try logging in again.
The issue was the latest instance in which glitches rendered Hotmail inaccessible. In March,users from accessing their accounts, leading some to speculate that the issue authentication software.
The company says Hotmail is the world's most popular Web e-mail service, boasting more than 145 million active users, as of January.