To disable automapping, use Windows PowerShell to remove full access permissions from the user for the mailbox, and then add back full access permissions to the user. When you add back full access permissions to the user, use the AutoMapping:$false
1. Run PowerShell
2. $UserCredential = Get-Credential
3. $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection
Import-PSSession $Session
4. Remove-MailboxPermission -Identity users-mailbox -User admins-mailbox -AccessRights FullAccess
Once you have removed the permissions run the following PowerShell command
Add-MailboxPermission -Identity users-mailbox -User admins-mailbox -AccessRights FullAccess -AutoMapping:$False
