function checkRequiredFields(input) {
	var x = document.forms[0].email.value;
	var filter  = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
	
	var requiredFields = new Array("achternaam", "voorletters",	"adres", "postcode", "plaats", "email");
	var fieldNames = new Array("Achternaam", "Voorletters", "Adres", "Postcode", "Plaats", "E-mail adres");
	var fieldCheck   = true;
	var fieldsNeeded = "\nDit contactformulier bevat een aantal verplichte velden. \nVult u aub de volgende ontbrekende velden in:\n\n\t";
	
	for(var fieldNum=0; fieldNum < requiredFields.length; fieldNum++) {
	if ((input.elements[requiredFields[fieldNum]].value == "") ||
	(input.elements[requiredFields[fieldNum]].value == " ")) {
	
	fieldsNeeded += fieldNames[fieldNum] + "\n\t";
	fieldCheck = false;
	}
	}
	
	if (fieldCheck == true)
		{
	
		if (filter.test(x)) {return true;}
			else
			{alert('Geen geldig e-mail adres!');
			return false;
		}
	}
	else
	{
	alert(fieldsNeeded);
	return false;
	}
}