the linux documentation project spam statz:

   93085   65.74%  DENIED_RDNS_MISSING
   21359   15.08%  DENIED_IP_IN_CC_RDNS
   13467    9.51%  DENIED_RDNS_RESOLVE
   10059    7.10%  DENIED_RBL_MATCH
--------------- Breakdown ---------------
    5041   91.55%  zen.spamhaus.org
     465    8.44%  bl.spamcop.net
-----------------------------------------
    2653    1.87%  ALLOWED
     725    0.51%  ERROR
     100    0.07%  DENIED_SENDER_NO_MX
      68    0.04%  TIMEOUT
      45    0.03%  DENIED_TOO_MANY_RECIPIENTS
      19    0.01%  DENIED_RELAYING

---------------- Summary ----------------
Allowed:     2653    1.87%
Timeout:       68    0.04%
Errors :      725    0.51%
Denied :   138134   97.56%
Total  :   141580  100.00%