You can allso query AD directly using ADODB
 Code:
CheckMailAdr("smtp:UserMail@@Domain.com")
  
Function CheckMailAdr($EMail)
	Dim $domCN,$Conn,$sLDAP

	If Not InStr($EMail,":")
		$EMail = "smtp:" + $EMail
	EndIf
	$domCN =  GetObject("LDAP://rootDSE").Get("defaultNamingContext")
	$Conn = CreateObject("ADODB.Connection")
	$Conn.Provider = "ADSDSOObject"
	$Conn.Open("ADs Provider")
	$sLDAP = "<LDAP://" + $domCN +  ">;(&(objectCategory=person)(proxyAddresses=" + $Email + "));adspath;subtree"
	$RecSet = $Conn.Execute($sLDAP)
	If $RecSet.RecordCount = 1
		$CheckMailAdr = $RecSet.Fields(0).Value
	Else
		$CheckMailAdr = ""
	EndIf
EndFunction

-Erik