[exim] block incoming mails from subdomains

Hi

i want block incoming mails with a lot of subdomains (SPAM) like that
subdomain.co.tk
*.subdomain.co.tk

i put that (in exim for cpanel) at the start:
domainlist host_reject_recipients = lsearch;/block.txt

and in the file block.txt i put this (for example):
*.tk
*.co.tk
co.tk


but do not work for me, i want reject the mail, do not send a message,
only drop the email.



thanks for your time