Morten wrote:
Hmmmm.... Well.... Since you used "eg.", I guess you are open to use different applications then listed. CentOS comes standard with Cyrus-imapd (it's on the install CD, and you can also install it using yum). Default configuraion uses system accounts to authenticate, but it is trivial to change it to authenticate against LDAP (for example). Exim comes standard with CentOS too.
The easiest and simples virtual mail setup is SME which is based on Centos 4. http://contribs.org.
Rock solid, email server installed and running in less than a hour. Unlimited virtual domains, IMAP, webmail, anti-virus, spam assassin...