To be honest, I've never tried POP over SSL. SSL stands for "Secure Sockets Layer", and is a system that is used with HTTP for secure web sites, and can also be used for POP to secure POP transactions. As of this writing, we have not tested a POP server with SSL functionality (still looking for a free one) and we don't know what the status is of client support. If anyone could help us in either of these areas, please let us know. I mention this as an "option" simply to point to something we could support at a future date.
We are aware of stunnel, but we haven't tried it out yet.
Looks like there's also a tutorial on how to do this for IMAP, which should also work for POP, but again, I haven't checked it out.
Another tool: SSLwrap.