[exim] SPAM with empty subject field

Lately we have been receiving a lot of SPAM with the empty subject
field.

I have searched the Exim 4 book and also the v4.6x spec pdf file looking
for a variable that holds an incoming message's subject as I want to do
a check in the acl_smtp_data ACL for this type of SPAM.

Is there such a variable?


My search of the pdf file found mention of the $h_subject variable.

Is this variable available in Exim?


Thanks


Paul McIlfatrick