DSBL is GONE and highly unlikely to return. Please remove it from your mail server configuration.
DSBL was a blocklist specialized in listing open relays and open proxies. To put it simply, DSBL listed IP addresses of computers that could be tricked into sending spam by anybody. This was a very successful strategy. Nowadays open relays and open proxies are rare, spammers hardly ever use them any more and no software seems to come with an open-by-default policy any more.