Postini, Google's suite of e-mail security, management and archiving services, encountered service disruptions on Tuesday afternoon and evening.
Google acknowledged the first problem shortly after 3 p.m. U.S. Eastern Time, saying that "a significant subset of users" had been rendered unable to access Postini services.
That problem, declared solved at around 5:30 p.m., didn't affect mail flow through the Postini system but did make the Administration Console and Message Center inaccessible, while notifications and alerts couldn't be delivered either, according to a note on the Google Apps Status Dashboard.
Later, between 8 p.m. and 10 p.m., about 34 percent of users faced similar issues, apparently as a result of routine maintenance work done on Postini software and hardware.
Postini's cloud-based e-mail services are available as stand-alone components and also as part of the broader Google Apps collaboration and communication suite, which is also Web hosted.
For cloud software to fulfill its promise of being more convenient for IT departments than on-premise applications, cloud vendors must reduce as much as possible service disruptions and performance issues. When vendor-hosted applications are unavailable frequently and for extended periods of time, IT departments often have to appease their angry end users while being unable to do much to solve the problem.
Postini also had performance problems on Friday, when about 10 percent of its users were unable to log into the Administration Console, Message Center and Message Archiving for about 45 minutes, although mail flow wasn't affected, according to the Apps Status Dashboard.
Also last week, Google announced it was waiving some fees for its App Engine hosted application development platform because the performance of product's datastore had been subpar for weeks.
The App Engine problems are expected to persist for at least two more weeks as Google scrambles to beef up the service's server infrastructure.