We have been running a production application on Azure for almost 3 years now that relies on web-hook notifications of incoming messages arriving on Office 365 mailboxes. Within the past day or so, we have noticed a significant percentage of messages for which we are not getting web hook notifications. All of our mailbox subscriptions are current and correct - a given mailbox may get 30 messages in an hour, and we may only see notifications from 25. We need to get notifications for 100% of them.
I want to emphasize that we have no reason to believe this is a programming issue - this portion of the application has not changed in months, and most of the time is working just fine. None-the-less, we have been told by Azure Support that the only means of getting production support for this issue is here at SO.