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MC395210: Microsoft Defender for Office 365: Recipient Block Using Tenant Allow/Block List Senders

Updated July 19, 2022: We have updated the rollout timeline below. Thank you for your patience.

Today, the Tenant Allow/block List is used to prevent users from receiving email from selected senders using the sender block. However, users are still able to send email to that email address or domain as recipient. With this update, the Tenant Allow/block List will be extended to prevent users from sending emails to these email addresses and domains that are added or part of the sender block list. This message is associated with Microsoft 365 Roadmap ID 93363.

Today the Tenant Allow Block List is used to prevent users from receiving email from select senders. However, users are still able to send emails to that same address or domain. With this new feature, the Tenant Allow Block List will be extended to prevent users from sending emails to addresses and domains that are added to the Allow/Block list.

MC395210: Microsoft Defender for Office 365: Recipient Block Using Tenant Allow/Block List SendersWhen this will happen

The rollout should start around late July (previously mid-July) and should be completed by late August (previously mid-August).

How this will affect your organization

This won’t apply to intra-organizational sender email addresses. It will apply to existing sender blocks and any new sender blocks which are added to the Tenant Allow/Block List.

If a user tries to send an email to these blocked senders, they will get the following NDR:

“- 5.7.1 Your message can’t be delivered because one or more recipients are blocked by your organization’s tenant allow/block list policy”

What you need to do to prepare

We advise you to cross check the existing sender block in Tenant Allow/Block list to ensure that it does not affect any sender that you want your users to send emails to, but can’t because of this change.

Message ID: MC395210
Published: 28 June 2022
Updated: 19 July 2022
Platform: US Instances, Web, World tenant

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