Exchange Online Protection (EOP) customers should be emailed when the list of EOP sending IPs changes
When the EOP sending IPs change some inbound emails bounce until the receive connector on our on-premise Exchange is updated to match.
But the only way to know that the EOP sending IPs has changed is to check a TechNet page (https://technet.microsoft.com/en-us/library/dn163581(v=exchg.150).aspx).
This isn't good enough. You know an EOP IP change will affect most of your EOP customers, so you should notify them directly.