Update: tcp_wrappers support has been obsoleted with version 1.3.10. For piler versions 1.3.10 and newer, use the smtp acl list feature.

To enable tcp_wrappers edit /etc/hosts.allow and/or /etc/hosts.deny to limit access to piler. Example hosts.allow file

piler: 11.22.33.44: ALLOW
ALL: ALL: DENY

Then if anything other than 11.22.33.44 tries to connect to piler, it will get the following error:

telnet piler.yourdomain.com 25
Trying 1.2.3.4...
Connected to piler.yourdomain.com.
Escape character is '^]'.
550 You are banned by local policy
Connection closed by foreign host.

You can see the following in syslog:

Oct 29 10:35:32 archivehost piler[23336]: connection from 123.123.123.123
Oct 29 10:35:32 archivehost piler[23336]: denied connection from 123.123.123.123 by tcp_wrappers