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How to Add All Shared Mailboxes to a Dynamic Microsoft 365 Group

Maira Mehtab Sep 20, 2026 869 views

Question details

An organization needs a reliable way to automatically add all shared mailboxes to a dynamic Microsoft 365 group without having to manually assign extension attributes to each new mailbox.

Product: Microsoft 365
Device & OS: not provided
Scenario: Automating Microsoft 365 group memberships to dynamically include shared mailboxes.
Observed behavior: Currently, administrators must manually assign extensionAttribute1 to new shared mailboxes for them to be picked up by the dynamic group.

Before you start

Ensure you have Exchange Administrator or Global Administrator privileges in your Microsoft 365 tenant, and verify that you have the appropriate Microsoft Entra ID (Azure AD) P1 or P2 licenses required to use dynamic groups.

Solution 1Recommended

Use Microsoft Entra ID Dynamic Membership Rules

Create a dynamic group rule that filters users based on specific attributes related to shared mailboxes.

Microsoft Entra ID (formerly Azure AD) allows you to create dynamic membership rules. While filtering natively by 'Shared Mailbox' recipient type can be tricky, you can often target synchronized on-premises attributes or specific naming conventions.

Access Microsoft Entra

Select or Create Group

Navigate to Groups > All groups. Click 'New group' or select your existing dynamic group. Ensure the Membership type is set to 'Dynamic User'.

Edit Membership Rules

Under the dynamic group settings, click 'Add dynamic query' or 'Edit' on the Dynamic membership rules section.

Configure the Syntax

Use the rule builder to filter members. If you sync from on-premises, you can match specific Active Directory properties. For cloud-only environments, consult Microsoft documentation or PowerShell community guides for the most effective property to query for shared mailboxes.

Save the Rule

Click 'Save'. The system will evaluate the rule in the background and automatically populate the group with matching shared mailboxes.

Solution 2

Automate Attribute Tagging via PowerShell Script

Use a scheduled PowerShell script to automatically locate shared mailboxes and tag them with the required extension attribute.

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Frequently Asked Questions

Do I need a special license to create dynamic groups in Microsoft 365?

Yes, utilizing dynamic group membership in Microsoft Entra ID (Azure AD) requires an Azure AD Premium P1 or P2 license for each user affected by the rule and for the tenant administrators configuring it.

Why is my new shared mailbox not appearing in the dynamic group immediately?

Dynamic group evaluation in Microsoft Entra ID runs periodically. Depending on the size of your directory and the complexity of your rules, it can take up to 24 hours for the group membership to fully update.

Can I use Exchange Admin Center instead of Entra ID for dynamic mailboxes?

Exchange Admin Center allows you to create Dynamic Distribution Groups specifically for email routing. However, if you need a Microsoft 365 Group (which provides a shared workspace, Teams integration, and SharePoint site), you must configure the dynamic rules via Microsoft Entra ID.

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