[exim] lsearch question

I have a text file that looks like this:

yahoo.com
aol.com
google.com
hotmail.com

I want to do some kind of search on this file to match $sender_host_name
against this list where the $sender_host_name ends in one of the domains
listed in the file.

How do I do that?

Thanks in advance for not saying RTFM