A majority of Google mail users were unable to access the service on Tuesday afternoon, in a rare widespread outage of the popular Gmail service.
Google said at 5:37 p.m. edt (9:37 GMT) that it fixed the problem but was still investigating the cause of the outage, which lasted for over an hour.
Users around the world appeared to be affected, with people from England, Italy, Singapore and South Africa reporting problems on the company's support site.
The outage comes as Google attempts to compete with Microsoft Corp and IBM to expand its service among business users, who are likely to be less tolerant of long outages.
Anyone thinking of migrating over to Google mail for business might want to think again! It's so annoying - free or otherwise! one user wrote on the support site on Tuesday.
Gmail already competes with Microsoft's Hotmail and Yahoo Corp's web-based e-mail.
Google offers its email service for free and also sells a version to businesses with extra features and technical support for $50 per user per year.
The fear of outages, in addition to security concerns, has been a reason many businesses are wary of adopting cloud computing technologies, being offered by Google as well as Salesforce.com and Amazon.com, which help deliver data and services over the Internet.
(Reporting by Ritsuko Ando, additional reporting by Jim Finkle and Edwin Chan; editing by Carol Bishopric)