[exim] Reject on helo

I am trying to reject a delivery based on the sender's helo name. I
get many concurrent connections where the helo consistently has the
same format (displaying a domain name for instance). So, I am
guessing these are mass mailing systems that don't bother altering
the helo.

I have smtp_accept_max_per_host = 5 to limit connections from the
same IP and still they insist by getting a different IP and using up
their five connections. Can`t see how this can be anything other than
spam. I could restrict the IP at acl connect but want to be less
strict in this case, so I set up a deny at acl helo as follows:

#       deny    message       = Your email has been rejected probably  
because your domain has been sending spam.
#       log_message   = HELO in reject_helo list
#       condition     = ${lookup {$sender_helo_name} \
#                               lsearch{/etc/exim/reject_helo} \
#                               {yes}{no}}

where /etc/exim/reject_helo contains, one per line: *baddomain1.com
*baddomain2.com, etc.

however, when I run a mock smtp connection with, for instance exim -
bh 192.168.11.22 and do EHLO baddomain1.com, I get

>>> deny: condition test failed
>>> processing "deny"
>>> check condition = ${lookup {$sender_helo_name} lsearch{/etc/exim/
reject_helo} {yes}{no}}

 >>>                 = no
 >>> deny: condition test failed

Is the condition set up properly, or am I approaching the issue in a
wrong way?

Thanks for the help.