I wanted to be in full control of mailbox migration, so my requirements were fairly strict:

• Don’t just submit all mailbox move requests en masse
• Submit move requests in “Suspended” status, so that I can manually release them at a later time
• Move smallest mailboxes first, and progress gradually to big mailboxes
• Chose best destination mailbox database
  • I define best as the database with the most free space.
• Only pull mailboxes from one mailbox database at a time

The script below will accomplish these objectives.

Keep in mind, your destination mailbox database is likely named differently than mine – make sure you change it on line number 21.

I’ll post the script I use to release these suspended jobs systematically at a later date.

$BatchSize = 5
$sourceMailboxDatabase = "Mailbox Database 1"

Write-Host "Creating Move Requests and Suspending them"

$allmbx = Get-Mailbox -database $sourceMailboxDatabase |
   Get-MailboxStatistics |
   Sort-Object TotalItemSize |
   Select-Object DisplayName,TotalItemSize
   $AllMBXCount = $allmbx.count

Write-Host "There are" $AllMBXCount "mailboxes to be migrated"
Start-Sleep -Seconds 8

$batch = 1
for ($i=1;$i -le $AllMBXCount;$i++)
{
	if ($i % $BatchSize -eq 0)
	{
		#write-host "Batch $batch" -ForegroundColor 'DarkCyan'
		$result = Get-MailboxDatabase -identity "DAG*" -Status |
                Select-Object name,DatabaseSize,AvailableNewMailboxSpace |
                Sort-Object -Property DatabaseSize
		$bestDatabase = $result[0].name
		$batch++
	}

	Write-Host "New Move - Batch:" $batch "-" $bestDatabase "/" $allmbx[$i].DisplayName -ForegroundColor 'DarkGreen'
	New-MoveRequest -TargetDatabase $bestDatabase -Suspend -Identity $allmbx[$i].DisplayName -BatchName "Batch $batch" | out-null

}

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