+20. If the key for a dnsdb PTR lookup is not an IP address, it is used
+ verbatim, without component reversal and without the addition of
+ in-addr.arpa or ip6.arpa.
+
+21. Two changes related to the smtp_active_hostname option:
+
+ (1) $smtp_active_hostname is now available as a variable. Its value
+ sticks with the message and is therefore available in routers and
+ transports at delivery time.
+
+ (2) The default for smtp_banner uses $smtp_active_hostname instead
+ of $primary_hostname.
+
+22. The hosts_max_try_hardlimit option (default 50) is added to the smtp
+ transport. Exim will never try more than this number of IP addresses; if it
+ hits this limit and they are all timed out, the message is bounced, even
+ though not all IP addresses may have been tried. Compare hosts_max_try,
+ which is a "soft" limit, because Exim will exceed it when hosts time out.
+ The new limit is a protection against lunatic DNS configurations with
+ hundreds of IP addresses.
+