MS exchange mx entry check using powershell

Hi,

There's this website that will be able to check the mx entries of our MS exchange server, and we want to write an exchange management shell script that will be able to emulate in doing so, below is the script;

$ie = New-Object -com InternetExplorer.Application
$ie.navigate("http://mxtoolbox.com/")
$ie.visible = $true
$doc = $ie.document
$tb1 = $doc.getElementByID("ctl00_ContentPlaceHolder1_ucMxActionInput_txtToolInputOldSchool")
$tb1.value = mydomain.com

When executing the .ps1 and ""Run it as Administrator", we get this error;

$tb1 = $doc.getElementByID("ctl00_ContentPlaceHolder1_ucMxActionInput_txtToolInputOldSchool")

You cannot call a method on a null-valued expression.

Server Info: IE 9 / Exchange 2010 / Windows server 2008 R2