People expect email to be as reliable as their phone's dial tone, and our goal is to deliver that kind of always-on availability with our applications. It's been a couple years since we blogged about the reliability of Gmail, so we thought we'd share some changes to our Google Apps service level agreement (SLA) and some new data.

Strengthening our SLA
We're pleased to make a couple changes that improve our SLA for our customers. Unlike most providers, we don't plan for our users to be down, even when we're upgrading our services or maintaining our systems. For that reason, we're removing the SLA clause that allows for scheduled downtime. Going forward, all downtime will be counted and applied towards the customer's SLA. We are the first major cloud provider to eliminate maintenance windows from their service level agreement.

We're also amending our SLA so that any intermittent downtime is counted. Previously, a period of less than ten minutes was not included. We believe any instance that causes our users to experience downtime should be avoided -- period.

Gmail: 99.984%
In 2010, Gmail was available 99.984 percent of the time, for both business and consumer users. 99.984 percent translates to seven minutes of downtime per month over the last year. That seven-minute average represents the accumulation of small delays of a few seconds, and most people experienced no issues at all. For those few who were disrupted for a longer period of time, we're very sorry, and Google Apps for Business customers received compensation where appropriate. We're particularly pleased with this level of reliability since it was accomplished without any planned downtime while launching 30 new features and adding tens of millions of active users.

Seven minutes of downtime compares very favorably with on-premises email, which is subject to much higher rates of interruption that hurt employee productivity. The latest research from the Radicati Group found that on-premises email averaged 3.8 hours of downtime per month. In comparison to Radicati's metrics for on-premises email, our calculations suggest that Gmail is 32 times more reliable than the average email system, and 46 times more available than Microsoft Exchange®.1

Fortunately Microsoft Exchange® customers can still benefit from the reliability of Gmail with Google Message Continuity. Comparable data for Microsoft BPOS® is unavailable, though their service notifications show 113 incidents in 2010: 74 unplanned outages, and 33 days with planned downtime.

Email is much more complex than your home phone, so making it as reliable as the dial tone is no mean feat. Despite our best efforts, we will have outages in the future. But we're proud of our track record so far and we're working hard to make it even better. Every time you reach for your phone you expect it to work. And we believe that is a worthwhile benchmark.

1. The Radicati Group, 2010. "Corporate IT Survey – Messaging & Collaboration, 2010-2011"

Update: clarification added to fifth paragraph.