LinuxHomeNetworking.com has simple, useful tutorials on all topics.
How to configure mail servers - http://www.linuxhomenetworking.com/wiki/index.php/Quick_HOWTO_:_Ch21_:_Configuring_Linux_Mail_Servers
You may prefer Postfix rather than SendMail, for reasons discussed in this Mail Server tutorial -
http://www.linux.org/threads/mail-servers.4224/ I use SSL on ports 587 and 993. ISP blocking of port 25 is not an issue.
