I would like to install an extremely small mail server on my VPS and I am only interested in it sending out mail (activation links) from my web site. I don't need it to support mailboxes or incoming mail (although having that option for the future might be nice).
The main requirement is that I don't have to worry about monitoring it as often and protecting against people bouncing messages off my server or wasting resources with incoming mail. I just want to send mail out. So something small that only listens on localhost would be ideal. The other requirement is that it is documented so I can learn how to set it up and manage it.