Hello, I can´t add members to an existing mail group of my ownership

Hello Ali Boscan,

Based on the information you provided, I understand that you are attempting to add members to a group that grants access to a mailbox, but you receive a 400 Bad Request error when trying to make the change.

From the screenshot you shared, it appears that your organization is using a hybrid environment with Active Directory (on-premises AD) synchronization. The group you are trying to modify is likely synchronized from your on-premises Active Directory to Microsoft 365.

In this scenario, synchronized groups are considered read-only in Exchange admin center, which means membership changes cannot be made through the Microsoft 365 Admin Center, Exchange Admin Center, or Azure/Entra portal. Any attempt to modify the group in the cloud may result in errors such as the one you are encountering.

To add or remove members, the change will need to be performed directly in your local Active Directory. Once the membership has been updated on-premises, the change should be synchronized automatically to Microsoft 365 during the next directory synchronization cycle.

If you are not the administrator responsible for managing Active Directory, I recommend contacting your IT or Active Directory administration team and asking them to update the membership of the group on-premises.

I hope this clarifies the cause of the issue. Please let us know if you have any questions or if you need help confirming whether the group is synchronized from on-premises Active Directory.

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