I probably misunderstand but why not just install an SMTP+IMAP server and add RoundCube/SquirreMail or similar? This should take like 15 minutes to do.
Since you talk about phpBB it sounds like you just want something users can log on to and do it, not necessarily tightly integrated in something else.
Since you talk about phpBB it sounds like you just want something users can log on to and do it, not necessarily tightly integrated in something else.
I feel like I'm missing something.