Can SURBL blacklist 4th level domains? "connexus.net.au" is a perfectly valid domain, but subdomains of "dsl.connexus.net.au" are a bit suspicious.

I got a spam referencing 106-147.dsl.connexus.net.au, probably someone running a webserver on their DSL connection.

Reading http://www.surbl.org/implementation.html and http://spamcheck.freeapp.net/two-level-tlds makes me think only 2nd and 3rd level domains can be blacklisted.

Am I wrong and/or is there any chance this will change? In theory, 3rd level domains like "connexus.net.au" could be added to two-level-tlds (ok, the name would have to change), and the implementation rule would be:

1) If the tail of your domain is listed in two-level-tlds, check one level deeper. Examples: if your domain ends in "guernsey.gg", SURBL-check "whatever.guernsey.gg"; if you domain ends in "connexus.net.au", check "whatever.connexus.net.au"

2) If the domain's not listed in two-level-tlds, check 2 levels deep (eg, "whatever.com").