Adding RBL's to exim on a cpanel server couldn't be easier, there are plenty of HOWTO's around for doing it but one thing I found when I was a new user trying to get my head around it was that the howtos tend to direct you to check the RBL's at the RCPT stage of an e-mail transaction, this ISN't the correct means of doing it and generates excess log noise with 'unexpected disconnection' messages. To factor these out you simply add an ACL check to the HELO/EHLO stage.(cPanel's exim config by default does not have this set up.)

Heres how you do it....

Go to the 'Exim Configuration Editor' in Web Host Manager and click the 'Advanced Editor' Button.

In the first box under '#!!# cPanel Exim 4 Config' add:

acl_smtp_helo = check_helo

Then scroll down to the ACL section of the editor, which has
'#!!# These ACLs are crudely constructed from Exim 3 options.
#!!# They are almost certainly not optimal. You should study
#!!# them and rewrite as necessary.

begin acl' above it

In the first of the three boxes add:

check_helo:
# Check sending hosts against DNS black lists.
# Reject message if address listed in blacklist.
deny message = Message rejected because $sender_fullhost \
is blacklisted at $dnslist_domain see $dnslist_text
dnslists = bl.spamcop.net : \
sbl.spamhaus.org : \
xbl.spamhaus.org : \
list.dsbl.org : \
zombie.dnsbl.sorbs.net : \
blackholes.mail-abuse.org : \
smtp.dnsbl.sorbs.net : \
web.dnsbl.sorbs.net : \
escalations.dnsbl.sorbs.net : \
nomail.rhsbl.sorbs.net : \
badconf.rhsbl.sorbs.net : \
http.dnsbl.sorbs.net : \
socks.dnsbl.sorbs.net : \
misc.dnsbl.sorbs.net
accept:

That is the list of RBL's that are the least agrovation in shared hosting environments, It is also a good idea to add some additional ACL's from Exim ACL Spam Filters (rossz's list)

Save the exim configuration and your all done!