Microsoft is carrying out an investigation on prevalent issues causing delays in Exchange Online email delivery. The technology giant has received complaints from users experiencing delays in receiving external emails early in the morning GMT +2. The issues seem to be affecting users globally, spanning across regions from the Americas to Asia and Europe. Microsoft assures that the errors are impacting only users that are served through the affected infrastructure.
Problems Traced to ‘Server Busy' Errors
The key issue causing delays is a “Server busy” error message indicated by ‘451 4.7.500 Server busy‘ error code. Microsoft has confirmed these ongoing challenges, linking them to specific infrastructural problems. The company is currently analysing sample throttling IPs from simple messages, with intentions to evaluate the impact of the infrastructure on the issue before devising a remediation plan.
We're currently working on a fix to address an issue causing delays receiving external email messages in Exchange. Additional details and updates will be provided in the admin center under EX680695.
— Microsoft 365 Status (@MSFT365Status) October 11, 2023
Anti-Spam Rules Enforcement Possible Cause
A recent service update to the infrastructure may hold the key to these persistent problems. Microsoft revealed in an update that erroneous enforcement of IP-address-related anti-spam rules could be the cause of the issue. This discovery aligns with claims from users stating that Exchange Online spam filter resulted in thousands of emails being added to the outbound queue.
As per the latest reports, the technology company has not yet confirmed the overall impact of the Exchange Online outage on outgoing mail delivery and neither has it established which regions have been affected. In the wake of these problems, Microsoft users and other interested entities are eagerly awaiting more updates and information disclosed under EX680695 in the Microsoft 365 admin center.
Recent Efforts to Boost Exchange Online Security
Earlier this month, Microsoft ended the Remote PowerShell Protocol in Exchange online. The company has made it clear that organizations will not have the option to continue with the use of RPS for Exchange Online. Microsoft is urging clients to shift from using RPS for Exchange Online and recommends the use of the Exchange Online PowerShell version 3 module instead.
In September, Microsoft brought enhanced security features to Exchange Online. The forthcoming enhancements encompass the integration of Domain Name System (DNS)-based Authentication of Named Entities (DANE) for SMTP and Domain Name System Security Extensions (DNSSEC).
