Shared Mailbox Member Management: Bulk Assign from User Profile & Intermittent First-Time Save Failure

The Exchange admin center already supports assigning one user to multiple shared mailboxes in one operation: select the shared mailboxes under Recipients > Mailboxes, then use Mailbox delegation to add that user.

Bulk-assign the user in the Exchange admin center

1. Open Microsoft 365 admin center > Admin centers > Exchange.
2. In the Exchange admin center, select Recipients > Mailboxes.
3. Select all shared mailboxes to which the user needs access.
4. Select Mailbox delegation.
5. Under Add a delegate, enter the user’s name or email address.
6. Under Select permission types, choose:
   • Full access — allows the user to open and manage mailbox contents.
   • Send as — allows messages to appear as though they came directly from the shared mailbox.
   • Send on behalf — identifies the user as sending on behalf of the mailbox.
7. Select Save.

Microsoft documents this multi-mailbox workflow directly in the EAC.^1^

This addresses the bulk-assignment requirement, although it is mailbox-oriented rather than located under Active users > user profile. Submit the requested user-oriented UI enhancement through the Feedback button at the bottom of the Microsoft 365 admin center; that form is Microsoft’s documented channel for admin-center bugs and feature enhancements.^2^

PowerShell alternative

For repeatable assignments, connect to Exchange Online PowerShell and apply permissions to a mailbox list. Access is controlled by Exchange Online RBAC, so the signed-in account must have the necessary mailbox-permission role.^3^

Connect-ExchangeOnline

$user = "[Email]"
$mailboxes = "[Email]", "[Email]"

foreach ($mailbox in $mailboxes) {
    Add-MailboxPermission -Identity $mailbox -User $user `
        -AccessRights FullAccess -InheritanceType All
    Add-RecipientPermission -Identity $mailbox -Trustee $user `
        -AccessRights SendAs -Confirm:$false
}

Add-MailboxPermission grants Full Access; Add-RecipientPermission grants Send As. These are distinct permissions—Full Access alone does not permit sending from the mailbox.^1^

Verify the assignments:

foreach ($mailbox in $mailboxes) {
    Get-MailboxPermission -Identity $mailbox |
        Where-Object User -Like $user
    Get-RecipientPermission -Identity $mailbox -Trustee $user
}

Disconnect-ExchangeOnline -Confirm:$false

Report the intermittent first-save failure

There is no confirmed current Microsoft-known issue in the available public information that exactly matches a first-attempt failure when saving shared-mailbox membership. The documented Microsoft 365 admin-center operation is still:

Teams & groups > Shared mailboxes > select mailbox > Members > Edit > Add members > Save.^4^

Because the failure is intermittent:

1. Go to Microsoft 365 admin center > Health > Service health.
2. Review Exchange Online incidents and advisories, including Issue history.
3. If no relevant issue appears, select Report an issue on the Service health page. This lets Microsoft correlate reports across tenants.^5^
4. Also submit the bug using the admin center’s bottom-of-page Feedback button.
5. If it continues, open Help & support, describe the issue, and select Contact Support. Microsoft recommends separate support requests for separate issues.^6^

Include the UTC timestamp, affected shared mailbox and user, browser, exact UI path, displayed error text, whether the second identical save succeeds, and how frequently it occurs. Avoid posting tenant identifiers or user details in a public forum.

References

1. Manage permissions for recipients in Exchange Online
2. Overview of the Microsoft 365 admin center
3. Connect to Exchange Online PowerShell
4. Configure shared mailbox settings - Microsoft 365 admin
5. How to check Microsoft 365 service health
6. Get support for Microsoft 365 for business