Find every instance of hostname

[Anne Wilson]

I have a small problem on my laptop which springs from the sender of an email 
being set as logwatch.localhost.localdomain.  I have so far been unable to 
find which config file needs editing to get the correct hostname, so I'd like 
to be able to search this box, where everything is fine, for config files 
that contain the box's hostname.  I could then check the list against the ones 
on the laptop.

It should be simple enough to do using find and grep, but I can't get a 
command that gives me the output I need.  How can I do it?

Anne