There's several tools for finding addresses but none of them can search every network and organization for the millions of people you can reach.
Mailing lists are similar to normal internet mail addresses. When you send to the lists address the mail is automatically multiplied and sent to every recipient of the list or in case of a moderated list to it's editor. The important thing to remember is that you shouldn't send subscription requests to the list address but to the address of it's maintainer which may usually be formed by attaching -request to the lists name (E.g. somelist-request@someplace.fi). In many cases public lists are managed with automatic mail servers called listservs, mailservers or the like in which case you should send mail to it's address (e.g. listserv@searn.sunet.se) with word HELP in the body if you don't have any other instructions on subscribing. Please also first look if the list is already gatewayed to some newsgroup like many of them are so you'll save many resources including your time...
And remember, if you know the domain part of the address pointing to the local "postoffice" there should be a human behind the local address postmaster(@someplace.someorg.fi) in every domain. The postmaster might sometimes be overloaded with error messages etc. so please try it only after all other methods for finding the address fail and use a meaningfull subject line to catch his or her eye.
The issue of addressing and related problems is too broad to describe in few lines but you could try the following tools.
Especially networks that are reachable via gateways may use different looking addresses internally which may be hard to search. If the resulting address looks strange or is clearly internal to some other network you could try to translate it to an Internet format.