Microsoft said it has mitigated an issue in its Office 365 service that automatically routed regular emails directly to users' junk folder instead of to their inbox.
“We're investigating an issue in which email is being sent to the junk folder,” the company said in an advisory at 7.20am AEST.
The company said at 8.47am that it had "reverted [a] change and observed successful email delivery."
"We're now reprocessing any emails that were incorrectly delivered as junk," it said.
iTnews’ own email accounts appeared to be impacted, with emails being incorrectly routed to junk since about 6.30am.
Enterprise users would be well-advised to check their junk folders for the past few hours.
Administrators reported trying to troubleshoot spam filtering settings on users’ accounts before the bug was acknowledged.
It is the second issue in the past 12 hours with Office 365 that was caused by the introduction of errant spam rules.
Though it was unlikely to have impacted A/NZ businesses greatly owing to the timing, last night Microsoft broke email forwarding for about three-and-a-half hours.
“We determined that a recently deployed spam rule is causing [the] impact,” it said.
“We've prepared a fix and are deploying it to the affected infrastructure.”
Users of the cloud productivity suite have become accustomed to frequent issues and rollbacks in recent months.
A major issue earlier this month rendered the body text of emails blank, and was not resolved for a number of hours.
There have also been a series of lockouts due to outages of Azure Active Directory.