[Exim] acl question

In exim 4.10, it is possible to do something like this?

deny          sender_domains  = aol.com
              message         = X-Forgery: NOT AN AOL MAILER ($h_X-Mailer)
              condition       = ${if match {$h_X-Mailer:}{.*[Aa][Oo][Ll].*} {no}{yes}}

I'd like to somehow harvest the X-Mailer in these messages.

Thanks,
Jeff

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