[Exim] acl to block sender HELO

on a typical log line like so:

2003-09-19 05:49:02 H=(mailin-04.mx.aol.com) [68.115.146.58] F=joe@???

what would you use in an ACL to deny on the "mailin-04.mx.aol.com" ?

It is my unerstanding that "senders" would be the F= line,
but I cannot glean the keyword I need for the "H=" line.

TIA
--
Jim Pazarena    mailto:paz@qcislands.net
                http://www.qcislands.net/paz