CheckFolderExists.ps1

function CheckFolderExists($folderToTest) {
    $mbxs = Get-Mailbox -PublicFolder
    Write-Output "Found $($mbxs.Count) public folder mailboxes"
    $good = @()
    $bad = @()
    for ($i = 0; $i -lt $mbxs.Count; $i++) {
        Write-Progress -Activity ($mbxs[$i].Identity) -PercentComplete ($i * 100 / $mbxs.Count)
        $result = $null
        $result = Get-PublicFolder $foldertoTest -Mailbox ($mbxs[$i].Identity) -ErrorAction SilentlyContinue
        if ($null -ne $result) {
            $good += $mbxs[$i].Identity.ToString()
        }
        else {
            $bad += $mbxs[$i].Identity.ToString()
        }
    }

    Write-Host "$($good.Count) mailboxes have it:"
    $good | Sort
    Write-Host "$($bad.Count) mailboxes don't have it."
}