User level: Level 1 (67 points)For some unknown reason, an email from a Microsoft 365 Business tenant with a calendar invitation (ics file) was blocked by iCloud servers.
De sender also received a bounce back email with de following url: https://learn.microsoft.com/en-us/troubleshoot/exchange/email-delivery/ndr/fix-error-code-550-4-4-7-in-exchange-online
The strange part is that I have had contact for a very long time with this person and organization.
Posted on Oct 7, 2026 2:14 PM
User level: Level 1 (23 points)Oct 12, 2026 12:00 AM in response to ImMartijn
It is not an 'unknown reason', it is the fact that Apple has not updated to the sync protocol of Microsoft from EWS to EAS. It has on iOS so there are no issues on iOS applications, they just failed to update Apple Mail and Apple Calendar. Microsoft has announced stopping with EWS a long time ago, over a year ago at least. On October 1, 2026 Microsoft turned off EWS by default on their systems. System managers can still manually opt in to keep their organisation on EWS for at most 6 months when it will be finally terminated with no way back. Apple knew that Microsoft would do this and failed to provide an adequate update before October 2026.
User level: Level 1 (67 points)Oct 12, 2026 12:36 AM in response to Gamick
This issue isn’t about the Apple Mail application. That’s another conversation.
My issue is about the iCloud servers that process the email traffic for iCloud Mail users.
Originally posted at discussions.apple.com/thread/256372142