"Lots of people around the world who rely on Gmail were disrupted during their waking and working hours, and we are very sorry. We did everything we could to restore access as soon as possible, and the issue is now resolved," said Gmail site reliability manager Acacio Cruz in a blog post.
Google had been testing new code designed to keep data geographically closer to its owner, which brought about disruption when maintenance in one datacentre caused another facility to be overloaded. This had a cascade effect, according to Google, and it took the company an hour to get it back under control.
"We know how painful an outage like this is. We run Google on Gmail, so outages like this affect us the same way they affect you," Cruz said.
In order to compensate customers for any lost business due to the outage, reports say that Google will offer 15 days of free service to businesses and organisations that pay for the email service.
The Gmail outage was not the only problem Google experienced on Tuesday. A phishing scam attacked the search firm's Google Talk chat service. Users were asked to "check out this video" by clicking on a link, but the URL directed users to a web site called ViddyHo which asked for Gmail usernames and passwords.
The scammers sending the links have now been blocked, and Google has blacklisted the ViddyHo site. Google Talk now carries a warning to users that entering any information on the page may result in identity theft or other fraud.
Also see: Cutting the Cable: how Offline Gmail makes webmail useful
Also see: How to avoid spending thousands on a mail server
Also see: Can Gmail Tasks solve your To-Do list nightmare?