[exim] Dkim + From + Sender

Hi

Actually, I have in exim.conf :

DKIM_DOMAIN = ${lc:${domain:$h_from:}}
DKIM_FILE = /etc/dkim/${lc:${domain:$h_from:}}.pem
DKIM_PRIVATE_KEY = ${if exists{DKIM_FILE}{DKIM_FILE}{0}}

I want to do :
How to detect DKIM from $h_sender, if no DKIM with $h_from ?

So something like....
if DKIM_PRIVATE_KEY==0
{
DKIM_DOMAIN = ${lc:${domain:$h_sender:}}
DKIM_FILE = /etc/dkim/${lc:${domain:$h_sender:}}.pem
DKIM_PRIVATE_KEY = ${if exists{DKIM_FILE}{DKIM_FILE}{0}}
}

or like ...
DKIM_DOMAIN = ${lc:${domain:$h_from:}}
DKIM_FILE = /etc/dkim/${lc:${domain:$h_from:}}.pem
DKIM_PRIVATE_KEY = ${if exists{DKIM_FILE}{DKIM_FILE}{DKIM_DOMAIN =
${lc:${domain:$h_sender:}}
DKIM_FILE = /etc/dkim/${lc:${domain:$h_sender:}}.pem
DKIM_PRIVATE_KEY = ${if exists{DKIM_FILE}{DKIM_FILE}{0}}}}


What would be the good syntax ?


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