V8/usr/src/cmd/upas/README

To make upas, perform 'make install' in the directories send, print and
rfc822.  The meaning of the directories is:
send: the program that becomes /bin/mail and /bin/rmail.
print:  the program used to print a user's mail (exec'd by /bin/mail)
rfc822:  programs to convert between UNIX format mail and RFC822
common:  routines common to any two of the above