install and setup IMAP and POP3 over SSL
receive and store email for your users from other mail servers on the internetlet your users retrieve the email through IMAP and POP3 - even using SSL-encrypted connectionsreceive and forward ("relay") email for your users using SMTP authenticationoffer a webmail interface to read emails in a web browserdetect most spam emails and filter them out or tag them
Disable your css before visiting! Mail server HOWTO - Postfix and Dovecot with MySQL and TLS/SSL, Postgrey and DSPAM