SARE is bad, it can cause problems with Cpanel and rules not being compatable, and all that fun stuff
Be simplistic, remove SA altogether, use ASSP instead. If you take a look @ the CPanel forums, you'll find two very well put together CPanel integrations, one paid, one not so
I ditched SA quite some time back, and saw a drastic decrease in server load. Of course I had (a few) SARE rules in place, but overall, no personal rules.
ASSP is a lightweight proxy, much like SA, only ASSP handles things much more efficiently than SA, and doesn't require any "extra" processing or filtering from exim.
Assp can look at multiple events as 'scoring' techniques, and can accept or reject mail based on one, or multiple RBLs, unlike the instances of exim / sa which (IIRC) bounce it if it's in only ONE list.
ASSP can handle user interaction, such as whitelisting, spam reporting, redlisting (don't ask me, I just say what it can do ), whitelist removal, etc, all with a simple email address. So, you can forward spam, or mislabeled (not)spam to the system and it learns from it's mistakes!
ASSP also automatically adds those you send mail to to it's whitelist so you're not constantly having to worry about 'will these guys be able to mail me', and does NO processingg on those addresses, unlike SA/exim which may (note: may) add them to the list, but will STILL process them through the other application (IE: SA adds them, but exim will still go through it's 'spam' processes). This is one of the key features of being a 'spam proxy' as opposed to what SA is.
With ASSP processing things, nothing needs to be processed by exim as far as 'spam control'. ASSP handles this all, much, much better than exim does, and if the mail is in fact spam, it'll not even botther to pass it on to the mail server.
I think you'll ffind that instead of adding more applications to the server, thusly adding more load to it, you will probably want to re-think that, and remove apps from the server, and add a competent spam processor to begin with.
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I do not run cpanel or any panel however, I have found you can eliminate 99% of spam by installing spamassassin, razor, pyzor, dcc. + smfzombie and several rbl (sorbs,etc) in sendmail. In addition, you need to train spamassassin ie create a mailbox to dump spam in and use the sa-learn function to train spamassassin periodically. I also use my address book as a whitelist for spamassassin.
I assume you can do the same thing with exim (vs sendmail). All of these things do put a load on the server but should not be too bad if you have reasonable memory / hardware.
I do run sare rules (rules_du_jour) and have not found them to be a problem.