Microsoft Office 365’s Exchange Online Protection (EOP) service now includes a new feature called IP throttling. Office 365’s new feature checks IP’s reputation, inspects the IP’s sending history, to allow a particular message.
Office 365 now makes use of basic IP throttling where sending email from a brand new IP is no longer advantageous; indeed, it now works against senders. For spammers, this is bad and for our customers, this is good. It means that this type of spam is greatly reduced (our internal statistics show a major decrease in spam from new IPs because of this). But the flip side is that there are lots of good senders that spin up email from new IPs, or have erratic sending patterns, but are not sending spam. Unfortunately, they sometimes trip up the same IP throttling patterns. We try to fix these as we encounter them.