The DNS host hMailServer should query when doing a DNS blacklist lookup.
The IP address that the DNS blacklist server will return if the senders IP address is found in the DNS blacklist. It's possible to use wildcards in the IP address. It's not possible to specify several different addresses such as 127.0.0.1 and 127.0.0.4. 127.0.0.* must be used in that case.
The message that hMailServer will give to the sending client if an email is rejected.