+PH/11 Callouts were setting the name used for EHLO/HELO from $smtp_active_
+ hostname. This is wrong, because it relates to the incoming message (and
+ probably the interface on which it is arriving) and not to the outgoing
+ callout (which could be using a different interface). This has been
+ changed to use the value of the helo_data option from the smtp transport
+ instead - this is what is used when a message is actually being sent. If
+ there is no remote transport (possible with a router that sets up host
+ addresses), $smtp_active_hostname is used.