Exchange Online mailboxes sync delay [office365]

This incident has been resolved.

Our systems have fully recovered. We are now retrying failed tasks.

Microsoft deployed a fix. Our systems are recovering.

Latest update from Microsoft:
> At 20:52 CET
> We're continuing to redirect traffic and apply targeted remediation to impacted servers.
> We've observed initially positive results in some areas, and we're monitoring service health closely as our mitigation workstreams continue in parallel.

Microsoft is deploying a fix

> At 15:27 CET
> We’re monitoring the progress of the fix, which has been deployed to approximately 60% of the affected environments. We’re continuing our manual restarts on the remaining impacted machines.

We are closely monitoring our systems for signs of recovery; however, we have not observed any significant progress at this time.

Microsoft is still investigating the issue; here is their latest update.

> We’re continuing to investigate recent changes, service telemetry and the failure paths to determine the root cause of impact.

Source: https://portal.office.com/Adminportal/Home#/servicehealth/:/alerts/MO941162 (You need to be an O365 admin to be able to access it)

Our partner Microsoft is experiencing a service degradation affecting Exchange Online mailboxes. You can follow Microsoft Issue ID MO941162 for more details. This may cause outbound/inbound delays for customers using Office 365, as Front cannot connect to Microsoft servers.