Implement Soft Greylisting
The bigger mail providers are sending the mails from its customers with different mail servers which are having different IP addresses to balance the load. But this is very difficult for a greylisting mechanism which is programed very strict. As a result some mails are coming through late or senders which are on the whitelist are blocked.
There is a mechanism around which is called "Soft Greylisting". For example: The last byte inside of an IPv4 address is not getting analyzed in the assumption that the mail server are normally together in a subnet.
I would like to get "Soft Greylisting" implemented AND the option to switch between strict and soft.
If you want to receive Office365 Emails in a timely manner, you must disable Greylisting checks for this sender. This would be *.mail.protection.outlook.com. But at the moment wildcards aren't allowed.