The hosted applications in Microsoft's Business Productivity Online Standard Suite (BPOS) have averaged uptime of 99.9 percent or better in the past year, according to the company.
BPOS, a collaboration and communications suite hosted by Microsoft and sold with partners, includes Exchange Online, SharePoint Online, Office Communications Online and Live Meeting.
Last week, Google touted a 99.98 percent uptime for its hosted Gmail service in 2010, for both individual account holders and people who use it as part of Google Apps, a BPOS rival. Google didn't provide the uptime rate for the other Apps suite components, like Docs and Calendar.
Google and Microsoft offer a 99.9 percent uptime guarantee for their Apps and BPOS suites, respectively. When that service level agreement (SLA) isn't met, Google offers affected customers credits and extends their subscriptions, while Microsoft offers cash reimbursement.
Google announced last week that it was modifying its SLA to count every instance of downtime; previously, it logged only outages of 10 minutes or more. It also tweaked its SLA to include outages due to planned maintenance work, which previously wasn't counted against the 99.9 percent uptime commitment.
According to a spokesman for Microsoft, the BPOS SLA counts "any service issue as downtime, from the minute it starts to resolution."
"We also count issues for any number of impacted users, not just if 'enough' users are impacted," he said via e-mail.
The competition between Google Apps and BPOS has been heating up in the past year. Google has been updating its suite with capabilities aimed at large enterprises and their CIOs. Google Apps has traditionally been aimed at small and medium-size businesses.
Meanwhile, Microsoft is beta testing a big upgrade to BPOS called Office 365, whose applications will be based on the latest 2010 versions of their on-premise counterparts. Office 365 will also include versions that come with Office Web Apps, a hosted version of Microsoft Office, and with the option of the full-featured Office suite itself.
Because BPOS and Google Apps are cloud-hosted suites, their performance and uptime are critical aspects to their respective customers, most of whom rely on the suites as their primary workplace e-mail service.