Google’s web-based email service GMail was unavailable for for about an hour yesterday, affecting up to 35 million users.

The outage was first acknowledged on Google’s Apps Status Board at about 17:40 GMT, and was resolved about one hour later.

The web giant initially reported that the outage was affecting "less than 2% of the Google Mail base". This would have been around 5 million people, based on Google’s claim that 350 million people use the service.

It later revised this number up to "less than 10%", meaning that up to 35 million users, including those that use Google Apps to run their business, were unable to access their emails for that hour.

"While we have resolved this issue with Google Mail, it’s possible that some users may experience message delays because affected accounts weren’t available to receive messages," Google wrote, offering no explanation for the outage.

Google guarantees a 99.9% uptime service level agreement, meaning that companies it must have fewer than 7.7 hours’-worth of outages per year. 

A number of large enterprises have signed up to Google’s hosted email and collaboration suite recently, including pharmaceuticals giant Roche and Spanish Bank BBVA – both with about 100,000 Gmail seats – and Hillingdon Council in the UK. Hillingdon Council told Information Age that they had not experienced an outage.