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Microsoft Office 365 – Secure by Default

Secure by default in Office 365

Secure by Default – Honoring EOP/ATP detonation verdictsMC226683

Major update: Announcement started

Applied To: All

We’re making some changes to how tenant (Anti-spam/Hosted Content Filter policy) and user (Safe sender) allows work when it comes to high confidence phish. A message is marked with the high confidence phish verdict when we detonate it and know that it is malicious. We want to ensure that our customers are protected and therefore block those messages from getting to the inboxes of end-users. This is normally the case, but tenant and user overrides can stop this from happening. We have decided to no longer honor Allowed senders or domains when the messages are considered as high confidence phish.

[Key Points:]

  • Timing: Beginning mid-December through the end of January 2021
  • Action: Review and assess impact

[How this will affect your organization:]

When this change is implemented we are going to update our filtering rules so that inbound messages that are considered high confidence phish and destined for Office 365 mailboxes will not honor anti-spam policy or Safe sender allows. Emails with other verdicts like (regular) phish, spam, etc will not be affected and the allows will still work as expected.

Note: adding senders and domains to an allow list is not best practice and should be considered as a legacy way of filtering. 

[What you can do to prepare:]

Administrators should use the submission portal to report messages whenever they believe a message has the wrong verdict so that the filter can improve organically.

Review, to learn more about Secure by default in Office 365.

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