Microsoft confirms this issue has been resolved, for more information see the Microsoft 365 Admin Center under EX1331830 (https://admin.cloud.microsoft/#/servicehealth/:/alerts/EX1331830).

During this time Signature 365 has been fully operational, all emails have been delivered with signatures.

Microsoft reports in EX1331830 that Exchange Online users are experiencing significant delays or failures when sending and receiving email messages in Exchange Online.

We have seen improvements in server wide delivery, this may be due to reduced traffic due to work time patterns.

We continue to monitor.

We are currently experiencing delays forwarding emails to Exchange Online, caused by degraded availability in Exchange Online Protection. This affects a subset of customers using server-side signature injection.

We are monitoring the situation