Q0733 - Exim/exim GitHub Wiki
Is there any way to tell Exim not to lookup the IP address against any DNS black list if the connection is over IPv6?
Use this condition in your ACL:
condition = ${if match{${mask:$sender_host_address/0}}\
{${mask:::0/0}}{no}{yes}}
From Exim 4.23 onwards, this can be simplified to
condition = ${if isip6{$sender_host_address}{no}{yes}}