Concurrent mailbox moves from Exchange 2007 to 2013

Question

We are in the process of migrating from Exchange 2007 to Exchange 2013. We have about 200 mailboxes and we want to move them in groups of 40-50 at a time. I am trying to get more then 1 mailbox to actually sync to the new database at once.
I start the batch with 49 mailboxes but only 1 mailbox is showing any progress when I go to details. They all have a status of "syncing" but only one has any "items synced".
I have run multiple articles about increasing concurrent migrations from 2007 to 2010 and 2010 to 2013 and they all mention going to MsExchangeMailboxReplication.exe.config on the destination server and setting the “MaxActiveMovesPerTargetMDB" value
to something larger. By default 2013 has it set to 20 would should be more than enough  for me. However despite this setting I still only see 1 mailbox syncing at a time.
Is there someplace I should be making a similar change on the 2007 box? I can't find a file with that name so I am not sure if there is something to change or if it's even needed.
Why is this not working? Any help is much appreciated. Thanks!

Answer 1

Outlook will show the infamous login popup and users will not be able to access Exchange 2013 Public Folders.
You can check the Outlook Clients version in Exchange Management Shell with Get-LoginStatistics (ex. Outlook 2010):
Get-Logonstatistics | select-object username,clientversion | where {$_.clientversion -gt "14.0*" -AND $_.clientversion -lt "14.0.6117.5001"}
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