[+] RBL Check option: Min. RBL positives. Proxy is blacklisted if number of RBL positives equal or exceed this value.

BTW, list of RBL services:

cbl.abuseat.org, dnsbl.invaluement.com, dnsbl.sorbs.net, dul.dnsbl.sorbs.net, smtp.dnsbl.sorbs.net, spam.dnsbl.sorbs.net, zombie.dnsbl.sorbs.net, dnsbl-2.uceprotect.net, pbl.spamhaus.org, xbl.spamhaus.org, bl.spamcannibal.org, ubl.unsubscore.com, combined.njabl.org, dnsbl.ahbl.org, dyna.spamrats.com, spam.spamrats.com, cdl.anti-spam.org.cn, drone.abuse.ch, dul.ru, short.rbl.jp, spamrbl.imp.ch, virbl.bit.nl, dsn.rfc-ignorant.org, spamguard.leadmon.net, netblock.pedantic.org, grey.uribl.com, ix.dnsbl.manitu.net, rbl.efnetrbl.org, blackholes.mail-abuse.org, dnsbl.dronebl.org, db.wpbl.info, query.senderbase.org, bl.spamcop.net, b.barracudacentral.org, ddnsbl.internetdefensesystems.com, http.dnsbl.sorbs.net, misc.dnsbl.sorbs.net, socks.dnsbl.sorbs.net, web.dnsbl.sorbs.net, dnsbl-1.uceprotect.net, dnsbl-3.uceprotect.net, sbl.spamhaus.org, zen.spamhaus.org, psbl.surriel.com, dnsbl.njabl.org, rbl.spamlab.com, ircbl.ahbl.org, noptr.spamrats.com, cbl.anti-spam.org.cn, dnsbl.inps.de, httpbl.abuse.ch, korea.services.net, virus.rbl.jp, wormrbl.imp.ch, rbl.suresupport.com, ips.backscatterer.org, opm.tornevall.org, black.uribl.com, multi.surbl.org, tor.dan.me.uk, relays.mail-abuse.org, rbl-plus.mail-abuse.org, access.redhawk.org, rbl.interserver.net, bogons.cymru.com