The issue should be fixed.
Please verify. Thank you.
Update 12/04/2019 14:27 PM 9 days
Microsoft is currently making changes to their new servers. It appears the 365 team is using *.prod.outlook.com for newer servers vs the previous rDNS name of *.outbound.protection.outlook.com . We have added the new host name to the allowed list which should fix it.
We will monitor the situation. Thank you!