[exim] denying my IP in helo, easy retry for spammers?

If I want to stop spam messages that use my IP in the helo,
would I be better off blocking at the door via a helo acl? (or would
this just be an easy retry for them using another helo?)

Or by accepting the message and letting SA or a different exim acl do
the job, so that is done stealth to the spammer?

Thansk.

Joe