Automapping is an Exchange & Exchange Online feature which automatically opens mailboxes with Full Access permissions in a delegate’s Outlook client.
Remove the access permissions. This also removes automapping.
Logon to Azure EOL (with MFA)
Business@contoso.ie is the mailbox being shared.
anna.grimm@contoso.ie is the account that has the access rights.
In EOL PowerShell
Remove-MailboxPermission -Identity “Business@contoso.ie” -User “anna.grimm@contoso.ie” -AccessRights FullAccess
Confirm
Are you sure you want to perform this action?
Removing mailbox permission Identity:”Business@contoso.ie” for user “anna.grimm@contoso.ie” with access rights “‘FullAccess'”.
[Y] Yes [A] Yes to All [N] No [L] No to All [?] Help (default is “Y”): select A
You might get this error
WARNING
Can’t remove the access control entry on the object “User” for the user account because the ACE doesn’t exist on the object.
So use
Remove-MailboxPermission -Identity “Business@contoso.ie” -User “anna.grimm@contoso.ie” -AccessRights FullAccess –Confirm:$false –BypassMasterAccountSid
Re-add the permissions but without Automapping
Add-MailboxPermission -Identity “Business@comtoso.ie” -User “anna.grimm@contoso.ie” -AccessRights FullAccess -AutoMapping:$false