function checkEmail(field) {
	var email_string=field.value;
	var reMail;
	reMail = /^[0-9a-z]([-_.]?[0-9a-z])*@[0-9a-z]([-.]?[0-9a-z])*\.[a-z]{2,4}$/;
	if (!email_string.match(reMail)) {
		field.focus();
		field.select();
		return false;
	}
}