Rather than using ${mask:...} in the exim config, we can let postgrey do
this on its own. Otherwise, it gets confused with ipv6 addresses using
dots instead of colons as separators, and crashes
(https://bugs.debian.org/867201).
protocol_name=${uc:$received_protocol}\n\
instance=${acl_m_grey}\n\
helo_name=${sender_helo_name}\n\
+<%- if scope.call_function('versioncmp', [@lsbmajdistrelease, '8']) <= 0 -%>
client_address=${substr_-3:${mask:$sender_host_address/24}}\n\
+<%- else -%>
+ client_address=${sender_host_address}\n\
+<%- end -%>
client_name=${sender_host_name}\n\
sender=${sender_address}\n\
recipient=$local_part@$domain\n\n