Issue with Exchange Admin Center

Good day

I have a new update regarding this issue:

Behavior matches known Microsoft Service Incident EX1466035.

• The issue affects some admins attempting to add or remove members from Distribution Groups.
• Distribution Group owners experiencing the same behavior are considered part of the same incident.
• The Microsoft Product Group (PG) is actively investigating.

As a current workaround, Microsoft recommends managing Distribution Group membership through Exchange Online PowerShell using cmdlets such as Add-DistributionGroupMember and Remove-DistributionGroupMember.

Reference:

Add-DistributionGroupMember (ExchangePowerShell) | Microsoft Learn

Remove-DistributionGroupMember (ExchangePowerShell) | Microsoft Learn

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You can also check the details of this incident yourself in the Service Health section of the Microsoft 365 Admin Center, as shown in the screenshot, and search for Incident ID EX1466035

https://admin.cloud.microsoft/#/servicehealth

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Besides, as the final status: "After the initial investigation, we’ve determined that this issue and further communications will be handled directly through the existing support case. Please see your support case for additional insights. This communication will expire in 24 hours."

It means that you may also submit a support ticket through the Microsoft Admin Center for direct assistance with this issue.

Ticket Support: In the Microsoft 365 Admin Center->Support->Help & Support. You can raise support ticket In Microsoft Admin Center by this link:

https://admin.microsoft.com/#/support/requests

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I will continue to monitor this issue and keep you updated if any new information becomes available.

Looking forward to hearing your update!

Hello Love, Tangela Gresham

The "Response Content is Null" error usually happens due to a temporary web glitch, or because the specific email list type cannot be modified through the standard Exchange portal.

Please try these two quick workarounds to add your new members:

1/ Try Incognito Mode (Fixes web glitches)

Open a new Private/Incognito browser window, log back into your admin/Exchange portal, and try adding the members again.

2/ Use the Entra Portal (For Security Groups)

If your list is a Mail-Enabled Security Group, sign in directly to the Microsoft Entra My Groups Portal. Find your group and add the members there.

If this issue still persists, please reply with the type of the email list. Your IT Admin may need to check your Owner permissions or update the list directly via PowerShell.

Looking forward to hearing from you.