Here is a script, that runs though you Exchange server, and return all permission on all folders in all mailboxes.

The script needs to be running from the Exchange management Shell, and will create a subfolder in c:\ call ExchangeMailboxPermission, where it will create a text file for all yours mailboxes.

#This script will return all permissions on all folders
#in all mailboxes
#
#Written by Kenneth Dalbjerg - http://www.kennethdalbjerg.dk
#
$FolderPath = 'C:\ExchangeMailboxPermission\'
if ((Test-Path -path $FolderPath) -ne $True)
{
New-Item $FolderPath -type directory
}

$mailboxes = get-mailbox -resultsize unlimited
foreach ($mailbox in $mailboxes) {
$alias = $mailbox.DistinguishedName
$username = $mailbox.SamAccountName
$SpecialExchangeFolders = "Top of Information Store|Recoverable Items|Deletions|Purges|Versions"
$mailboxfolderes = Get-MailboxFolderStatistics -folderscope all -identity $alias | where { $_.name-notmatch $SpecialExchangeFolders }
$File = $FolderPath + '\' + $username + '.txt'
$mailboxfolderes | foreach {
$folder = $username + ':' + $_.folderpath -replace "/","\"
echo $folder
Get-MailboxFolderPermission -identity $folder
} | Out-file $File
}