Unless you really know what you are doing, leave it alone.
+ 4. If not built with DISABLE_DNSSEC, Exim now has the main option
+ dns_use_dnssec; if set to 1 then Exim will initialise the resolver library
+ to send the DO flag to your recursive resolver. If you have a recursive
+ resolver, which can set the Authenticated Data (AD) flag in results, Exim
+ can now detect this.
+
+ Current status: work-in-progress; $sender_host_dnssec variable added.
+
Version 4.80
------------