Preset policies have suddenly started notifying users of quarantined messages

It might have been roadmapped and scheduled, but this change is nonetheless unwelcome. Turning on user quarantine access should be an organisation's decision, not one mandated by Microsoft (even if just as a default). For one thing there is the additional support burden, and for another there are the colossal numbers of phishing attempts spoofing quarantine notices of all shapes and sizes (not just EOP). There is also the fact that it's sometimes harder to recognise a malicious mail in quarantine than in an Inbox. Want a Socratic defence? Don't enable user quarantine access.

I believe that ideally the default policies should be tougher than the actual policies in use for typical users, especially if the tenancy is sufficiently active and dispersed for a new accepted domain to be added without proper consideration. I hear what is said about the pre-set policies engaging new features that some customers might miss. This particular case argues the opposite. Certainly read the roadmap when you can, but I know that I don't always get time to.