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For Google, the issue was its consumer blogging service, Blogger, which was inaccessible or slow for most of Thursday. Early Friday, a Blogger status post indicated that 30 hours of posts, dating back to 7:37 a.m. PDT on Wednesday, had been removed to facilitate a fix.

Later on Friday, Blogger began restoring those posts and the service is now operating normally. In an apologetic blog post, Blogger tech lead Eddie Kessler attributed the problem to data corruption.

Microsoft has been experiencing problems for the past few days with its Business Productivity Online Suite (BPOS), a set of online applications that includes Exchange Online, SharePoint Online, Office Communications Online, and Office Live Meeting.

On Tuesday morning, the company's BPOS-S Exchange service had trouble dealing with malformed email traffic.

"Exchange has the built-in capability to handle such traffic, but encountered an obscure case where that capability did not work correctly," explained Dave Thompson, corporate VP of Microsoft Online Services in a blog post. "The result was a growing backlog of email."

The backlog lasted several hours for some customers, but has been resolved. Then on Thursday, malformed email again tripped up BPOS-S Exchange, resulting in the delay of some 1.5 million messages. This second backlog was also resolved in a matter of hours.

The email issues were compounded by an unrelated DNS server problem early Thursday morning, which, for about three hours, prevented customers from using Outlook Web Access hosted in the Americas, and also had some impact on Microsoft Outlook and Microsoft Exchange ActiveSync devices.

As with the widely reported Amazon Web Services outage in April, the dominant theme of complaints has been not the lack of access but the lack of communication about service restoration efforts.

Thompson acknowledged this in his blog post and promised a more detailed post-mortem. "As a result of Tuesday's incident, we feel we could have communicated earlier and been more specific," he wrote. "Effective today, we updated our communications procedures to be more extensive and timely. We understand that it is critical for our customers to be as fully informed as possible during service impacting events."

Thompson said Microsoft will continue to rely on its Service Health Dashboard to communicate about issues affecting its online suite of services. Microsoft's dashboard, unlike Google's publicly accessible Apps Status Dashboard, is accessible only to registered customers.

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