Google's Gmail service suffered a global crash yesterday, leaving the site inaccessible for around two and a half hours.
The service, which is used by over 113 million people, went down at around 9:30am GMT. The problem affected users of the free consumer offering, as well as business customers. It was Google's sixth outage in eight months and its longest ever.
The failure also affected users of web applications service Google Apps.
Google's engineers are still investigating the cause of the problem, Gmail Site Reliability Manager Acacio Cruz said in the Google blog.
"Our priority was to get you back up and running," Cruz said. "We did do everything to restore access as soon as we could."
Google has offered its corporate customers - who pay $50 annually for a business package including an enhanced version of Gmail - 15 days worth of free credit in compensation, the Huffington Post said.