This tutorial shows how to set up an Ubuntu Natty Narwhal (Ubuntu 11.04) server that offers all services needed by ISPs and hosters: Apache web server (SSL-capable), Postfix mail server with SMTP-AUTH and TLS, BIND DNS server, Proftpd FTP server, MySQL server, Courier POP3/IMAP, Quota, Firewall, etc. In the end you should have a system that works reliably, and if you like you can install the free webhosting control panel ISPConfig 2 (i.e., ISPConfig runs on it out of the box).