And this is where my eyes glaze over. There is no shortage of vintage Terminal and e-mail software that runs on a Mac 128K and especially 512K. In fact I'm not even sure why someone would write such an application unless they were just screwing around and wanted to. I already use MacTerminal (which emulates vt100) to transfer files in and out of OS X using SheepShaver and napbar has confirmed ZTerm directly in OS X works with MacTerminal.
For me the idea is not necessarily getting the BBS experience ... I think Luddite even actually maintains an old dialup system. For me, it's about expanding the functionality of a 128K (and bragging rights). Obviously the technology exists to convert terminal-based mail-apps input/output to SMTP/Pop3 to be sent and received over the modern internet. Putting it together in a simple package that just works under OS X is another matter. What I don't want to do is actually dial-up anything. I simply want to be able to log onto my Mac and start sending and receiving e-mail.
For many non-UNIX users on this forum, these kinds of projects usually die a quick death since it involves some advanced configuration of tools which are not familiar to most Mac users, not because they can't be done. I guess what I'm looking for is a step-by-step which I understand. Anyway, it's a fun idea that's beyond my skill set.