TrinityOS is a step-by-step, example-driven HOWTO on building a very functional Linux box with strong security in mind. TrinityOS is well known for its strong packet firewall ruleset, Chrooted and Split DNS (v9 and v8), secured Sendmail (8.x), Linux PPTP, Serial consoles and Reverse TELNET, DHCPd, SSHd, UPSes, system performance tuning, the automated TrinityOS-Security implementation scripts, and much more.
CD Linux Server is an embedded Linux system on a bootable live CD. It can be used to set up mail, Web, file, FTP, proxy, DHCP, DNS, MySQL, LDAP, and other services very quickly. The mail server includes antivirus, antispam, and mail recorder features. It can be used for free for up to 10 accounts, while the advanced version is licensed for an unlimited number of users. There is not any restriction against the time.