[Identified] We have identicated that mails send to the following domains are bounced by Microsoft.
We will repair this issue and come back to you as soon as possible.
August 3, 2020 17:18 BST August 3, 2020 16:18 UTC
[Investigating] Ticket was opened at Microsoft to delist the IP address.
August 12, 2020 06:10 BST August 12, 2020 05:10 UTC
[Resolved] Microsoft said that the IP was never blocked.
So the incident was a temporary failure of mail delivery to outlook.
The service works now!