Should your correspondents embed hostnames in their aliases, changes of host or hostname will catch them. This is not gryphon, or portal, or AOL, nor do we wish that kind of reputation on the net. The folk here are mostly computing or other scientific professionals. Snooping in others' directories, net.flames, long signatures, and other asocialialities are not appreciated. Users are guests in a communal home, and are expected to act responsibly.
Security is a very serious concern.
Use of the internet is a privilege. Attempting ssh, telnet, or login access to others' accounts or machines where you have no account, net scans or probes, etc. are cause for immediate loss of privileges. Passwords must be secure. A password checker is run periodically, and folk with crackable passwords get only one warning. Keep your directory 711 and your umask conservative, e.g. 077.