Google goes to everywhere on the web and puts everything in their database. So it also goes to the forums and listing of IP adresses and sites or domains that people complain about or have problems with.
It is an old trick - but not everybody uses it - to check yourself or better to check what others are saying about you.
So if you wanne know if others have a problem with your network you don't know about, try these tricks
make a list of your public servers with your domain, your Ip adresses, your mailadresses and than try the following searches
ex 128.147.123. will show what any user of your network has done on the web and that has been publicly published in counters, IP indicators or blocklists. This is also very useful in discussions about Wikipedia. If you have a problem convincing your CEO that you need to limit the internet usage of your network users than try your public IP and probably you will find some reasons....
ex if your mailserver is for example this 184.108.40.206 ( a known Chinese spamserver) than just inserting this in Google will give links to spamlists with this server on
You can also add things as 'proxy' to see if you have an open proxy
Instead of an Ip address you can also use your @domain or .domain
There is no better indexer of all the complaint forums, blacklists and whitelists (for abusers) than Google. Google is the mirror at which you ask, "mirror mirror on the wall, do I have a problem I don't know about at all ?"