Exim and I did get along quite well in the past, well at least mostly,
as it usually was quite well behaving. Unfortunately exim and I do have
a dispute over the appropriate behavior regarding smtp_active_hostname.
The documentation states (v4.87) for smtp_active_hostname:
At the start of an incoming SMTP connection, its value is expanded and
used instead of the value of $primary_hostname in SMTP responses.
While this seems reasonable it does seem to imply that no expansion
takes place whenever neither smtp is used nor a connection is coming in.
Unfortunately I had to realize that exim still expands
smtp_active_hostname for locally incoming mail. Does this even make
sense and is this behavior really intended?