Google says that Gmail is only used by tens of millions.

Although occasional failures are common, wider issues that have engaged the services of Google have been unusual. They are becoming a bigger threat to Google as it tries to sell more services to businesses.
Businesses are increasingly inclined to Google services because they are distributed on the internet, instead of being dealt within the facilities of each company. This can save companies money and bring more storage capacity than otherwise would have to buy.

But many companies have been skeptical about the advisability of outsourcing these tasks externally. Google argues that Web-based services are more reliable than those operated within business facilities, but large faults, such as Tuesday, represent another challenge to convince these companies reluctant.
Google said that more than 1.75 million businesses use Gmail as part of Google Apps, Google's answer to business software from Microsoft Corp. It is a crucial part in Google's strategy to root its brand among companies . Google Apps costs $ 50 per user per year.

It was not immediately known what caused the problem on Tuesday which led to Gmail users receive an error message while your computer tries repeatedly to connect to the service. The company said it is investigating the case.