Third Party Migration Tools & Exchange 2010 Default Throttling Policy

While migrating from GroupWise to Exchange 2010 SP1 with Quest GroupWise Migrator for Exchange (GME) I've experienced throughput issues. GME throughput (GB/hour) was decreasing more and more. Event Viewer errors on Exchange Server:

Process Microsoft.Exchange.AddressBook.Service.exe (PID=1636). User 'Sid~XXXXX\name-of-migration-account~RCA~false' has gone over budget '346' times for component 'RCA' within a one minute period. Info: 'Policy:DefaultThrottlingPolicy_4debe28f-3b74-4c7d-83c7-0650cb781f87, Parts:AD:345;'. Threshold value: '100'.

Solution:
1) New-ThrottlingPolicy "Quest GME Throttling Policy" -RCAMaxConcurrency $null -RCAPercentTimeInAD $null -RCAPercentTimeInCAS $null -RCAPercentTimeInMailboxRPC $null

2) Set-Mailbox name-of-migration-account –ThrottlingPolicy "Quest GME Throttling Policy"

3) Restart Microsoft Exchange Throttling service on Exchange Server

Re-Create the Discovery System Mailbox

According to Re-Create the Discovery System Mailbox:

'Multi-Mailbox Search uses a system mailbox to store discovery search metadata. This Discovery system mailbox has the display name SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9}. Because system mailboxes aren't visible in the EMC or in Exchange address lists, they are rarely deleted inadvertently.
However, if the Discovery system mailbox is deleted accidentally, discovery managers will be unable to perform discovery searches or manage existing discovery searches. In this case, to enable discovery functionality, you must re-create the Discovery system mailbox.'

My comments:
However, the Discovery Search Mailbox has not been created after re-creating the Discovery System Mailbox. To create the Discovery Search Mailbox:

enable-mailbox discoverysearch* -Discovery