Security News > 2023 > October > Exchange Online mail delivery issues caused by anti-spam rules
Microsoft is investigating Exchange Online mail delivery issues causing "Server busy" errors and delays when receiving emails from outside organizations.
According to user reports online, the Exchange Online problems started this morning, affecting Microsoft 365 customers worldwide, across the Americas, Europe, and Asia.
Microsoft confirmed the ongoing issues this morning, at 6 AM GMT+2, saying that "Some users may encounter delays receiving external email messages in Exchange Online. Affected users may see a '451 4.7.500 Server busy' error message."
More information on these ongoing Exchange Online issues is available under EX680695 in the Microsoft 365 admin center.
Microsoft has yet to confirm the regions affected by this Exchange Online outage and if it also impacts Exchange Online outgoing mail delivery.
Today's incident follows multiple Exchange Online outages blocking customers worldwide from accessing their mailboxes and sending or receiving emails since the start of the year.