The operation failed because UPN value provided for addition/modification is not unique forest-wide.

Is your request related to a problem? Please describe.
Seen a few cases on this, should add this to collect as well

Describe The Request
It appears we will attempt to create critical system mailboxes. We try to find them based off the Last Name. If admins delete the Last Names of the system mailboxes, it causes this issue.

Additional context

          $arbMbxname = "SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9}";
          $arbMbxLastName = "MsExchDiscovery e0dc1c29-89c3-4034-b678-e6c29d823ed9";
          $arbUser = @(Get-User -Filter {LastName -eq $arbMbxLastName} -IgnoreDefaultScope -ResultSize 1);
          if ($arbUser.Length -eq 0) 
          {
            $arbUser = @(Get-User -Arbitration -Filter {LastName -eq $arbMbxLastName} -IgnoreDefaultScope -ResultSize 1);
          }

          if ($arbUser.Length -eq 0)
          {
            Install-UserAccount -Name $arbMbxname -LastName $arbMbxLastName;
          }