diff --git a/smmapdfw/verify_worker/verify_worker.c b/smmapdfw/verify_worker/verify_worker.c
index 5907154..8f8cee7 100644
--- a/smmapdfw/verify_worker/verify_worker.c
+++ b/smmapdfw/verify_worker/verify_worker.c
@@ -733,6 +733,7 @@ static void *worker_thread(void *arg) {
   static const char *NOT_AN_ADDRESS = "not an email-address, no @ in it";
   static const char *DEFAULT_ANSWER = "default answer";
   static const char *NO_MX_AVAILABLE = "no MX available";
+  static const char *ILLEGAL_MX_ADDRESS = "0.0.0.0 can not be used at all";
   static const char *NO_PERM_RESULT = "no checker returned permanent result";
   static const char *INTERNAL_ERROR = "verifier internal error";
 
@@ -767,6 +768,9 @@ static void *worker_thread(void *arg) {
       if (NULL == mx_ip_addresses) {
 	wt->output = (char*) NO_MX_AVAILABLE;
 	result = SMM_LOCAL_PERM_NOK;
+      }	else if (0 == *mx_ip_addresses) { /* 0.0.0.0 is strange enough for a special case */
+	wt->output = (char*) ILLEGAL_MX_ADDRESS;
+	result = SMM_LOCAL_PERM_NOK;
       } else {
 	for (i = 0; (*(mx_ip_addresses+i) != 0) && (i < wt->vwh->vch->max_checker_threads); i++) {
 	  unsigned int address = *(mx_ip_addresses+i);