greylist()
  A greylist policy scanner.
  
  This is an greylist implementation for sagator.
  You can learn more about greylisting at:
    http://www.salstar.sk/sagator/greylisting/
  
  Usage: greylist(min=300, expire=48*3600,
           info_url="http://www.salstar.sk/sagator/greylisting/")
  
  Where: min is minimum required seconds after an email is cleanly sent
           (default: 5 minutes)
         expire is record expiration time in seconds (default 48 hours).
           If this record will be passed after min time, expiration
           time will be disabled.
         info_url is an string, which is displayed to greylisted clients
  
  Example: greylist()
  
  New in version 0.8.0.