Microsoft scrambled to fix a global outage that hit its Windows Live Hotmail service for several hours on Thursday.
The company said in a blog posting that "service has been restored for all users" around 5 p.m. Eastern Time and that it was "taking steps to make sure this doesn't happen again." It also apologized to Hotmail users for the inconvenience but did not say what caused the problem.
Hotmail users across the globe Twittered widely about the outage, which Microsoft said it first began hearing reports of at around 12 p.m. Eastern Time.
Twitter users said they were receiving a "Server is too busy" message when they tried to log into Hotmail, which has more than 375 million active users worldwide, according to Microsoft.
The Twitter reports were so widespread that Microsoft even sent out a message on its own WindowsLive Twitter feed letting people know it was aware of the outage, and then again when the outage was repaired.
This was the second outage for a major online e-mail service this week. On Monday, Google's Gmail service went down for as many as 24 to 36 hours for some users.
For Microsoft and Google, which are competing to bring more Web-based services to consumers and businesses, e-mail has been a proving ground for how many users their online services can support. Outages raise questions about the ability of those companies and other online service providers to maintain a consistent quality of service for end-users.