The RHSBL (right hand side blocking list) blackhole.securitysage.com appears to have been created by Jeffrey Posluns and appears to have been around since at least August, 2004.
I received a report today indicating that a mail administrator has been unable to reliably query the blackhole.securitysage.com DNSBL zone. With the help of my friends, I was able to confirm this issue.
It looks to be a DNS issue. What we see from here is that the zone blackhole.securitysage.com is delegated to nameserver blackhole.securitysage.com. The two DNS "glue entries" for the zone are servers that aren't configured to be authoritative for the zone, so no results are returned. Ultimately, this points toward a DNS configuration issue with this domain and/or sub-domain.
The popular anti-spam filter SpamAssassin has been tracking this issue since at least October 8, 2007. On October 17th, SpamAssassin decide to remove support for this list (implemented in the DNS_FROM_SECURITYSAGE rule), due to the ongoing issues with accessing this DNSBL.
As a result of this ongoing issue, I recommend against using the blackhole.securitysage.com blocking list. If you continue to check against this list; queries are likely to time out and it could delay the receipt of inbound mail. Use of this list while this issue persists is likely to provide no blocking or filtering benefit.
I, and others, have contacted Security Sage and Mr. Posluns, making him aware of the issue and asking for more information. I'll be sure to update this page with more information as I have it.
11/03/2007 update: I've seen no response to my email to Mr. Posluns, nor to a friend's email to Security Sage's support address. I emailed that support address today, and my attempt bounced. The error message suggested an SPF failure. The fact that I publish a working SPF record, and other information in the bounce, suggest that it is in error. I guess that means either nobody's home, or they don't want anyone to contact them.
5/26/2008 update: Way back in November, I talked to Jeffrey Posluns. He is no longer actively involved with Security Sage, but was kind enough to nudge the folks running things, in hopes of making things better. It fell off my radar, until a few days ago, when I was alerted to the fact that Security Sage's domains have expired.
Net result: Broken blocklist. Has a wildcard listing, meaning that if you use their list, you're probably negatively impacting your own email delivery.
My recommendation: Stop using this blocklist immediately and permanently. Even if they do somehow manage to pull things back together, they don't have a good track record of staying online.