450 Requested action aborted [7.2] 20412, please visit www.messagelabs.com/support for more details about this error message.
It took a remarkably large amount of searching to find out what ‘[7.2]’ meant in this error message, and why we kept getting a mailserver’s IP blacklisted, but if this happens to you, hopefully this will help resolve it.
When MessageLabs returns a [7.2], this seems to mean that they’ve checked the IP address of the host which is connecting to their MX against the CBL. Connections will be dropped immediately, rather than mail being rejected, as such:
# telnet cluster8a.eu.messagelabs.com 25 Trying 18.104.22.168… Connected to cluster8a.eu.messagelabs.com (22.214.171.124). Escape character is ‘^]’. 450 Requested action aborted [7.2] 20412, please visit www.messagelabs.com/support for more details about this error message. Connection closed by foreign host.
The easiest way to get around this is to fix your mail server, then request delisting from the CBL.
In a completely unrelated note (ahem), it seems that you may be added to the CBL if you send an email from a domain where the sending mail server is explicitly disallowed by SPF records (such as -all with no matching include), to a gmail address; Google will automatically (?) submit the IP address to the CBL and your problems will begin (again).
I highly recommend robtex as a lazy way to check your hosts against blacklists.