1.8 Possibly forged hostname for failed IP address here
This feature should probably not be set if you relay based on IP addresses in the
access database, because the feature does not look in that database.
7.6.6 FEATURE(use_client_ptr)??”V8.13 and Later
The check_relay rule set (?§7.1.1 on page 252) is used to screen incoming network
connections and accept or reject them based on the hostname, domain, or IP
address. The check_relay rule set is called with a workspace that looks like this:
host $| IPaddress
The host name and IP address are separated by the $| operator. As of V8.13, this
FEATURE(use_client_ptr) causes a new rule to be inserted as the first rule under the
check_relay rule set, which substitutes the value of the ${client_ptr} macro
(?§21.9.23 on page 813) for the prior host value passed.
Essentially, this causes V8.13 sendmail to behave like earlier versions of sendmail that
did not use the delay_checks.
7.7 Pitfalls
??? If your site supports dial-up clients or machines that are assigned an IP address
on startup, you should prevent such machines from sending mail directly to the
outside world. If you fail to take this precaution, you might find such machines
sending spam email that you can neither detect nor control. The easiest way to
limit mail access to the world is with a firewall or router. Make it your published
policy to always configure your firewall or router to prevent access to port
25 for all but your main mail hub machines.
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