Preset policies have suddenly started notifying users of quarantined messages

teetotal_mike the planned changes from Microsoft applied to both strict and standard policies.

(Updated) Exchange Online Protection: Bulk Filter (BCL) Improvements
MC467231 · Published Nov 15, 2022 · Last updated Feb 7, 2023

ADMIN IMPACT
FEATURE UPDATE

Message Summary
Updated February 7, 2023: We have updated the rollout timeline below. Thank you for your patience.
Exchange Online Protection (EOP) assigns a bulk complaint level (BCL) to inbound messages from bulk mailers. A higher BCL indicates a bulk message is less likely to be wanted by the user.
We are rolling out several changes in how we allocate BCL scores to messages to provide more accurate scoring and coverage for bulk messages. We are also updating the threshold for the strict policy from 4 to 5 to better align with the new scoring. In addition, customers using Microsoft Defender for Office P2 or customers with E5 licenses will be able to view the BCL score for a message in advanced hunting.

When this will happen:
We will begin rolling out in mid-November and expect to complete rollout by late April (previously January).

How this will affect your organization:
This change is expected to improve the handling of bulk messages within your organization and should not impact users. In the case of aggressive bulk settings where the threshold is 4 or less, may result in wanted bulk messages being called bulk and it is recommended that such policies be reviewed.

What you need to do to prepare:
There is nothing you need to do; however, it is good practice to review your Antispam policies to ensure that you have an appropriate value for BCL, particularly if you have a threshold of 4 or less.