[exim] $sender_host_address

If at first you don't succeed, try, try again.

The chapter on variables says $Sender_host_address is null for local
host. If the message arrives from 0.0.0.0 $sender_host_address contains
0.0.0.0. Likewise, 127.0.0.1, etc..

Therefore, the example shown in Chapter 31.11 WILL NOT WORK.

However, this conditional rewrite rule does work correctly:

  apache@* "${if match_ip {$sender_host_address}{@[]} \
     {postmaster@$1} {apache@$1} }"  Ffrs