Binary package “proftpd-mod-dnsbl” in ubuntu focal

ProFTPD module mod_dnsbl

 ProFTPD module for mod-dnsbl (DNS Black-List/Block-List)
 .
 A DNS blacklist is a way in which the DNS can be used to
 "blacklist" sites/addresses that have been deemd to be
 "bad" in some way. These blacklists are often used by
 email servers, for determining and rejecting email sent
 by addresses known to be sources of spam.