See INSTALL file

Note for slackware installations:
Be sure to install the extra descrypt.tgz software. vpopmail
uses the crypt function and it's not installed by default.

Note for IRIX installation:
1) change vfork to fork in vpopmail.c and opensmtp.c. 
2) delete all the -llibraries in the Makefile. 
3) add -I../ucspi-tcp-0.84 to the CFLAGS line

