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This IP address is HELO'ing as "localhost.localdomain" which violates the relevant standards (specifically: RFC5321).
The CBL does not list for RFC violations per-se. This particular behaviour, however, correlates strongly to spambot infections, and it is listed for that reason. Even if it isn't an infection, it's a misconfiguration that should be fixed, because many spam filtering mechanisms operate with the same rules, and it's best to fix it regardless of whether the CBL notices it or not.
There is often confusion between the SMTP "banner" and the SMTP "HELO" (or EHLO) command. These are completely different things, and proper understanding is important.
First some terminology (somewhat simplified to aid understanding):
A "SMTP client" is a piece of software that makes SMTP connections to SMTP servers to send a piece of email to the server. Most E-mail servers consist of an "SMTP listener" (to listen for and handle connections made to them by SMTP clients), an SMTP client (to send emails to other mail servers) and a local delivery agent (LDA) to deliver email to "local" users (eg: via POP or IMAP).
Thus, SMTP clients make connections to SMTP listeners, and issue SMTP commands to the listener.
The "HELO" (or "EHLO") command (see RFC2821) is a command issued by the SMTP client to an SMTP server to identify the name of the client. "HELO mail.example.com" means, essentially, "Hi there, my name is mail.example.com".
The "SMTP banner" is what the listener says in response the initial connection or in response to the HELO command.
The CBL works in many cases by seeing what SMTP clients say (in the HELO/EHLO command) when the client connects to a CBL detector. Since the CBL NEVER does SMTP probes, it has no way of knowing how a given IP banners.
You can test SMTP banners with telnet and other similar diagnostic tools, but you CANNOT test SMTP HELO/EHLO with telnet.
For that, you can send an email to email@example.com. That will reject the email (as an error), and the error will show you what the HELO/EHLO was.
If this IP is a mail server: please read namingproblems to find out why your IP was listed, and ways to fix it so it doesn't relist.
This IP is infected (or NATting for a computer that is infected) with a spam-sending infection. In other words, it's participating in a botnet. If you simply remove the listing without ensuring that the infection is removed (or the NAT secured), it will probably relist again.