spf.go
func (s *SPF) incVoidLookupCount(amt int) error {
	s.voidLookupCount = s.voidLookupCount + amt
	if s.voidLookupCount >= VoidLookupLimit {
		return &PermError{fmt.Sprintf("Domain %v exceeds max amount of void lookups: %v", s.Domain, VoidLookupLimit)}
	}
	return nil
}
func (s *SPF) incVoidLookupCount(amt int) error {
	s.voidLookupCount = s.voidLookupCount + amt
	if s.voidLookupCount >= VoidLookupLimit {
		return &PermError{fmt.Sprintf("Domain %v exceeds max amount of void lookups: %v", s.Domain, VoidLookupLimit)}
	}
	return nil
}
/* RFC 7208:

   As described at the end of Section 11.1, there may be cases where it
   is useful to limit the number of "terms" for which DNS queries return
   either a positive answer (RCODE 0) with an answer count of 0, or a
   "Name Error" (RCODE 3) answer.  These are sometimes collectively
   referred to as "void lookups".  SPF implementations SHOULD limit
   "void lookups" to two.  An implementation MAY choose to make such a
   limit configurable.  In this case, a default of two is RECOMMENDED.
   Exceeding the limit produces a "permerror" result.
*/