The following article aims into installing and configuring a simple POP3/IMAP/SMTP mail server in your Debian VPS using Postfix, Dovecot and SASL.
What is Postfix? It is a drop in replacement for the old and mature Sendmail. Postfix also attempts to be very fast, easy to administer, and secure.
What is Dovecot? It is an open source IMAP and POP3 server for *NIX-like systems, written primarily with security in mind.
What is SASL? SASL, the Simple Authentication and Security Layer, is a generic mechanism for protocols to accomplish authentication.