For now, Jha shared that the Exchange Online outage, which lasted roughly from 9 a.m. to 6 p.m. U.S. Eastern time, was triggered by a directory partition that stopped responding to authentication requests. This failure brought down Exchange Online for a "small set" of customers, but due to its "unique nature" it took Microsoft engineers a long time to fix it.
"Unfortunately, the nature of this failure led to an unexpected issue in the broader mail delivery system due to a previously unknown code flaw leading to mail flow delays for a larger set of customers," Jha wrote.
Meanwhile, Monday's Lync Online outage was triggered by a brief loss of client connectivity in Microsoft's data centers due to "external network failures."
"Even though connectivity was restored in minutes, the ensuing traffic spike caused several network elements to get overloaded, resulting in some of our customers being unable to access Lync functionality for an extended duration," Jha wrote.
Microsoft is taking steps to prevent these specific issues from affecting Exchange Online and Lync Online again, according to Jha.
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