Dovecot poolmon for modern IO::Socket::SSL (Cernko, Patrick)

This is a fork of DSI Centrale Méditerranée's poolmon (originally published by Brad Davidson) with which adopts the code to modern IO::Socket::SSL perl module.

Newer versions of IO::Socket::SSL validate the hostname used for establishing the connection against the X509v3 Subject Alternative Name field of the server's certificate. As poolmon used the IP address (provided by dovecot director status), this validation will fail unless the IP addresses are also included in the server's certificate. The modified version of poolmon provided here, has to options to fix this:

1. --resolve-hostname will do a reverse DNS lookup on the IP address and use the found hostname.
2. --no-hostname-verify will instruct IO::Socket::SSL to disable hostname validation when connecting to the server.

It is recommended to use the first option! The second option --no-hostname-verify only works by weakening the SSL security.

The current version of my poolmon can be found here:

• https://gitlab.mpi-klsb.mpg.de/pcernko/poolmon