I wanted to log as much useful information as I could from a Avaya phone system to my CentOS 7.x syslog server running rsyslogd.

That was easy, as I may noted before here:

# vi /etc/rsyslog.conf
…
if $fromhost-ip startswith ‘aaa.bbb.ccc.ddd‘ then /var/log/mylog.log
& ~

…

# systemctl restart rsyslog

However, I found my log flooded with the same unneeded messages over and over. To prevent those message from being logged into any of the log files, I made the following configuration changes:

# vi /etc/rsyslog.conf
…
:msg, contains, “what I want to filter out” ~
…

# systemctl restart rsyslog