I've been trying to configure the zen mailhosts, but spamcop hasn't seen all mailhost aliases for zen.
For instance if you compare the mx records for zen.co.uk (as seen at http://www.robtex.com/dns/zen.co.uk.html) with the standard "Zen Internet" mailhost config in spamcop, some servers are missing.
For instance, the lack of the following server is preventing me from submitting some spam:
212.23.6.48 bastion02.mail.zen.net.uk
While I have tried to force other mail server in the pool to register, by sending multiple e-mails, the only server spamcop registration e-mails pass through is bastion01.mail.zen.net.uk