Spamcop.net was one of the first blacklists. Fas founded in 1992 and in 2007 Spamcop.net became Cisco service. SpamCop is primarily a DNS blacklist, but also offers e-mail filtering.
SpamCop main method to maintain the list is obtaining spam from end users. Spam is analyzed and if meet listing criteria then SMTP server is included to SpamCop blacklist.
SMTP server IPs are listed if some spam was received from them. Spam analysis is done by humans at first. Then spam is parsed and tested to prevent false positive listing. SMTP server reputaion is tested - if is an open relay or open proxy, or if is on the SpamCop internal whitelist.
Notification emails with delisting instruction are sent to the postmaster@ and abuse@ addresses of the domain holder after blacklisting. IP addresses are delisted automatically after 12 hours. Recurrent listing extends the delisting time.
bl.spamcop.net returns 127.0.0.2 IP address to a reverse query if requested IP address is blacklisted.
Removal process is simple. You have to lookup the IP address and request it's delisting. If server IP has bad reputation delisting proces may take longer.