This is the IMAP4rev1 server from the University of Washington.
Included are backwards-compatbile (almost) POP2 and POP3 servers.

        ipop2d           POP2 daemon
        ipop3d           POP3 daemon
        imapd            IMAP4rev1 daemon

The ipop2d, ipop3d, and imapd daemons should be invoked by your
/etc/inetd.conf file with lines such as:

pop2    stream  tcp     nowait  root    /usr/local/libexec/ipop2d   ipop2d
pop3    stream  tcp     nowait  root    /usr/local/libexec/ipop3d   ipop3d
imap    stream  tcp     nowait  root    /usr/local/libexec/imapd    imapd