The "pop3d" command:

Usage: fossil pop3d [OPTIONS] REPOSITORY

Begin a POP3 conversation with a client using stdin/stdout using
the mailboxes stored in REPOSITORY.

If launched as root, the process first enters a chroot jail using
the directory of REPOSITORY as root, then drops all privileges and
assumes the user and group of REPOSITORY before reading any content
off of the wire.

  --logdir  DIR        Each pop3d session creates a new logfile
                       in the directory DIR and records a transcript
                       of the session there.  The logfile is opened
                       before entering the chroot jail.