[Exim] Accepting relay ONLY IF from-address is valid ??

Hi,

Is this possible? I userstand that relay_from_hosts and
relay_from_domains just allow mail to be sent from those
domains/hosts...

I have users connecting from all sorts of places and need a
way to get my server accepting any mail from anywhere for
delivery IF the from-address is valid (which should be looked-up
in a mysql table)

can anyone please help me?
I currently have this which works well for incoming mail:

domainlist local_domains = ${lookup mysql {SELECT data_domain FROM domains \
                           WHERE access_mail='1' and data_domain="${domain}"
}}

domainlist relay_to_domains = ${lookup mysql {SELECT data_domain FROM
domains \
                              WHERE access_mail='1' and
data_domain="${domain}" }}

thanks,
Andrew

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