Just don't learn at the expense of others. A badly configured server can cause collateral damage, both in increasing SPAM and blacklisting innocent users that have IP addreses 'near' yours.
Agreed. Personally, to me the best way to learn if you want, is to set up your internal network as an intranet. For instance, I have mydomain.com which is now hosted and independent of all my junk at home. Here at home, I have mydomain.intra. What I do in here affects no one but me and my (ever patient) wife. To be honest, even with our five computers I don't even bother running anything much other than Samba, so that we can keep our stuff on a RAID, as my wife has some horrible curse with failing disks. Even name resolution I just set up host files, because with the 4 systems I would want to access by name it is not worth setting up DDNS.... But you can set up your own internal DNS server, use Dynamic DNS, secure pop, secure smtp, Samba, and anything else you want, and not run the risk of bothering anyone else on the internet, or invoking the wrath of your ISP.
With a couple of machines, Fedora, and VMware Server and/or Xen you can set up two domains in your house firewall them behind iptables firewall with virtual networks, send mail back and forth between them, learn to lock them down, and everything else under the sun... You can make a mess fast and make no one want to slam their head against a desk but you. You can also download Solaris 10, FreeBSD, and Novell Netware (they have a 5 User unlimited time Demo out there somewhere on their site), Windows Server 90 day licenses and so on and really keep yourself busy. Set up NFS, RIS and Software Distribution Servers, Samba servers for Windows Clients; your options, and ability to learn, are virtually limitless with a couple computers these days... and really if you can learn to hop on any *nix or windows/whatever system, and have a good fundamental knowledge of networks, you only make yourself more valuable. It won't teach you everything there is to know about a corporate network, but it will get you on your way... beside being able to sit in front of a Novell, Windows, Linux, BSD, Solaris, or Mac system, and feeling comfortable is a good feeling.
