[Exim] ban connecting host

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Im trying to deny connections based on hostname. Ive added the following to
my config file, but it doesn't appear to be working:

  deny    hosts         = partial-lsearch;/usr/exim/hostban

the contents of the file are:

*.pipex.net
*.pipex.com

and the connecting host is in the form of blah.pipex.com

where am i going wrong?
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