Dropping the veil of secrecy over Office 365 uptime, Microsoft has released availability data for each of the past four quarters and is celebrating the results.
Between July 2012 and June 2013, the overall quarterly uptime for the cloud-hosted email and collaboration suite hit 99.98 percent, 99.97 percent, 99.94 percent and 99.97 percent, Microsoft said on Thursday in a blog post.
Those percentages are calculated based on the number of minutes in each calendar month and the number of minutes in which the Business, Government and Education editions of Office 365 were available worldwide.
"Individual customers may experience higher or lower uptime percentages compared to the global uptime numbers depending on location and usage patterns," the blog post reads.
Previously, uptime information was available only to Office 365 customers, but from now on Microsoft will report this data publicly on a quarterly basis.
The Office 365 components measured for uptime are Exchange, SharePoint, Lync and Office Web Apps "weighted on the number of people using each of these services," according to the blog post.
Gartner analyst Matt Cain said this move is "long overdue" because until now prospective Office 365 customers had a tough time getting this data, which is critical for making an informed decision on whether to sign up for the suite or not.
However, he cautions customers to treat this data with care.
"Because the data is rolled up quarterly -- as opposed to monthly -- and because it covers multiple workloads, and the three vertical market instances -- .gov, .edu and .com -- it is a very large-grain data point," he said via email. "Individual organizations can and will sustain outages."
Still, on the whole, "the numbers did indicate an acceptable degree of reliability," he added.
It's not clear from the blog post whether the SkyDrive cloud storage service is included in the uptime measurements.
Office 365 Pro Plus isn't contemplated in the calculation because it's a cloud-delivered and cloud-updated version of the Office productivity suite that's nonetheless installed on users' local devices.
The Office 365 service level agreement (SLA) is for 99.9 percent uptime, and calls for Microsoft to compensate customers financially if that guarantee isn't met.
Juan Carlos Perez covers enterprise communication/collaboration suites, operating systems, browsers and general technology breaking news for The IDG News Service. Follow Juan on Twitter at @JuanCPerezIDG.