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

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

When this will happen:

The rollout should start around mid-July and should be completed by 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


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I've been working with Microsoft Technologies over the last ten years, mainly focused on creating collaboration and productivity solutions that drive the adoption of Microsoft Modern Workplace.

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