DBMail is the only mail server I know that uses a MySQL backend to store messages: http://www.dbmail.org/ http://www.dbmail.org/ It does run on OSX. You'd the

DBMail is the only mail server I know that uses a MySQL backend to store messages: http://www.dbmail.org/ http://www.dbmail.org/ It does run on OSX. You'd then need to install a webmail client which can talk to DBMail via IMAP. Most of them work this way. My personal favourite is called Roundcube: http://roundcube.net/ http://roundcube.net/ It's written in PHP. Of course, you'd need to install a web server too.