func validateEmail(address string, resolver core.DNSResolver) (err error) {
	_, err = mail.ParseAddress(address)
	if err != nil {
		err = core.MalformedRequestError(fmt.Sprintf("%s is not a valid e-mail address", address))
		return
	}
	splitEmail := strings.SplitN(address, "@", -1)
	domain := strings.ToLower(splitEmail[len(splitEmail)-1])
	var mx []string
	mx, _, err = resolver.LookupMX(domain)
	if err != nil || len(mx) == 0 {
		err = core.MalformedRequestError(fmt.Sprintf("No MX record for domain %s", domain))
		return
	}
	return
}