5/22/2007 Update: Some of this information is out of date. Please click here for my latest thoughts on Spamcop and the Spamcop SCBL.
Recently, while doing a bit of research to find other opinions on blacklists, I ran across this seemingly random anti-blacklist blog post. He’s mad at Spamcop, but he thinks there’s some sort of collusion with Microsoft (and he even accused me of working for Microsoft—ha). Then he throws in a bunch of stuff about CAN-SPAM (missing the bits where it says that ISPs are free to block whatever they want in their best efforts to stop spam) and MAPS (which hasn’t blacklisted him and has no connection to the issue; he just wants to highlight that MAPS is free to define spam “outside of accepted standards,” as basically anyone in a society with a right of free press is allowed to do.)
Anyway. In this rant, he points out that Microsoft is using Spamcop. (February 2008 update: Previously I included links and info on Spamcop being controversial and causing significant false positive issues. Since then, I've made my own measurements that suggest Spamcop is fairly conservative and to be trusted.)
Microsoft is indeed using both the Spamcop Blacklist (SCBL) and the Spamhaus SBL-XBL combined feed. I emailed an address referenced in a bounce snippet posted on that other guy’s blog, and got an autoreply back indicating that Microsoft is indeed using both blacklists. Click here to see for yourself. Note that this is for mail sent to microsoft.com users only. This does NOT MEAN that MSN Hotmail is using Spamcop or Spamhaus. In other words, Microsoft the company is using it on their own mail, not as a filter on your Hotmail account.