check recipient addresses with Exim backup MX

Question

I want to configure backup MX with Exim on Debian, using dpkg-reconfigure exim4-config I've set this:

#update-exim4.conf.conf
dc_eximconfig_configtype='internet'
dc_other_hostnames='xxx'
dc_local_interfaces='127.0.0.1 ; ::1'
dc_readhost=''
dc_relay_domains='domain_to_relay'
dc_minimaldns='false'
dc_relay_nets=''
dc_smarthost=''
CFILEMODE='644'
dc_use_split_config='false'
dc_hide_mailname=''
dc_mailname_in_oh='true'
dc_localdelivery='mail_spool'

it accepts all mail going to the domain_to_relay, but I want to reject mail for unknown addresses (maintaining a list of known addresses) so it does not become a backscatter, how can I configure this?

The equivalent in postfix would be

relay_recipient_maps = hash:/etc/postfix/relay_recipients

Answer 1

I've solved this adding this to update-exim4.conf.conf

CHECK_RCPT_LOCAL_ACL_FILE=/etc/exim4/custom_acl

creating the custom ACL file /etc/exim4/custom_acl:

deny !recipients = /etc/exim4/recipients_whitelist

and creating the list of known addresses on /etc/exim4/recipients_whitelist

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