This issue has been resolved and all queues have now been processed. We will continue to monitor the situation and urge all customers to apply the Connection Filter instructions in this KB article to prevent it affecting them if it happens again:

We are working with Microsoft support to resolve this issue which is a throttle being applied at the O365 end. In the meantime, the issue can be mitigated by applying the connection filter listed here:


We are currently experiencing delays on inbound email. Delivering email into our customer's Office 365 tenants from our cluster is currently running slow due to a network issue at the O365 end. Engineers are investigating the issue. No email will be lost and any delayed will queue safely on the servers in the cluster until we can deliver it or the issue is resolved.

Began at:

Affected components
  • Email Security
    • Europe