Matt Whiting wrote:
Are you required to use an ISP in your country of residence?

Obviously not. But if you look at the "Path:" header of his posts you see:

Path: sn-us!sn-feed-sjc-03!sn-us!sn-feed-sjc-02!sn-xt-sjc-11!sn-xt-sjc-06!
sn-xt-sjc-12!supernews.com!postnews.google.com!news3.google. com!
news.germany.com!ecngs!feeder.ecngs.de!news.hotze. com!not-for-mail

What that mess means is the post originated from a machine named
news.hotze.com. Using a "whois" lookup indicates that the registrar query
URL for that domain is http://whois.tucows.com and plugging hotze.com into
the query field yields the information that the domain is owned by Martin
Hotze of Innsbruck, Tirol, Austria and provides a street address and phone
numbers.

So although Martin will not volunteer his postal address on the net, he is
hardly looking to make himself invisible. Of course a similar technique can
be used to locate my postal (home) address but I'm hardly looking to remain
difficult to find.