Hmailserver
'hMailServer is a free, open source,
GPL-licensed e-mail server for Microsoft Windows. It
supports all the common e-mail protocols (IMAP, SMTP and POP3) and comes with an easy-
to-use COM library that can be used for integration with other software. It also has support
for virtual domains, distribution lists, antivirus, antispam, aliases, distributed domains and
much more. E-mail data is stored in a database server, MySQL or MS SQL, depending on your
choice.
The hMailServer installation contains a minimal MySQL-installation, so if you don't already
have a database server in your network, MySQL is installed automatically when you install
hMailServer.'
Complementa-o com o squirrelmail como webmail e tens o assunto resolvido.