en Passant

 
#Pull all mailboxes from Source DB
$fromdb = get-mailboxdatabase -server Exch1 | ?{$_.storagegroup -match "lit hold"}
$sourcegrp = Get-mailbox -resultsize unlimited -database $fromDb

#Maximum amount of mailboxes to move.
$maxmbx = 100gb

#Some book keeping variables.
$currentsize = 0
$movegroup = @()
$index = 0
$undersize = $True

#Start picking mailboxes to move.
do {
        $me = $sourcegrp[$index]       
                     #Get Mailbox Size.
        $ms = get-mailboxstatistics $me.distinguishedname
        if ($ms -ne $null) {
                $mbxSize = $ms.totalitemsize.value.tobytes()
        } else {$ms = 0}
                     #Add mailbox to group as long as under Limit.
        if (($mbxSize +$currentsize) -lt $maxMbx) {
                $moveGroup += $me
                $currentsize += $ms.totalitemsize.value.tobytes()      
        } else {
                $UnderSize = $false
        }
        $index++
                     #Some on-screen reporting.
                     write-host $me,($currentsize /1gb), $ms.totalitemsize     
} while ($undersize -and $currentsize -lt $maxMbx -and $index -lt $sourcegrp.count)

#Find location to move to.
$bestdb = get-mailboxdatabase -server Exch1| ?{$_.storagegroup -match "lithold2"}

#Move mailboxes, 24 at a time.
$status = $MoveGroup | Move-Mailbox -TargetDatabase $bestdb.identity -BadItemLimit 600 -MaxThreads 24  -preservemailboxsizelimit -confirm:$FALSE

#generate reporting... Need to copy code from other script.. :)