======Spam Filter Rules: StartDNSBL======
^Statement  |StartDNSBL |
^Version  |2.2.1+ |
^Purpose  |Begins an asynchronous DNS blacklist lookup in advance of the result being required in a subsequent [[spamrules_statement_dnsbl|DNSBL]] statement |

The **StartDNSBL** statement requires a hostname and DNSBL zone, in the format
  StartDNSBL <hostname> <DNSBL zone>

The DNS blacklist lookup begins immediately, but the script is allowed to continue. When the **DNSBL** statement is reached, the script will get the result of the corresponding **StartDNSBL** statement. If the DNS blacklist lookup is still in progress, it will allow the lookup to complete, before returning the result.


=====Example=====
<code>
StartDNSBL ${SenderIP} sbl.spamhaus.org

# Continue with the rest of the script, whilst also running the DNS blacklist lookup

# By the time the script reaches the DNSBL statement, the lookup should either be fully or partially completed.

DNSBL ${SenderIP} sbl.spamhaus.org dnsresult
</code>