The firstLineMatch in the Mail bundle is '^From: (?=\w+@[\w-]+.\w+)', which doesn't match addresses with names. For example, the first line of my emails is 'From: Grant Hollingworth grant@antiflux.org'.
I changed the match to '^From: .*(?=\w+@[\w-]+.\w+)' (i.e., check for an email address somewhere on the line).