$validDomains = "*example.com", "*test.com", "*abc.com"
Get-QADUser -IncludedAttributes "proxyAddresses" | foreach {
	$account = $_.Identity
	$_.proxyAddresses | foreach {
		if ($_ -notlike $validDomains[0] -and $_ -notlike $validDomains[1] -and $_ -notlike $validDomains[2]) {
			$address = $_
			if ($address -like "SMTP*") {
				Write-Host "Removing SMTP address $_ from $account"
				Set-QADUser -Identity $account -ObjectAttributes @{proxyAddresses=@{Delete=@("$_")}} -whatif
			}
		}
	}
}