Ordinarily, the manual pages are formatted when sendmail, or one of the companion programs, is built. These preformatted manuals are the ones installed in the cat manual directories when the program is installed. This confINSTALL_RAWMAN macro causes the unformatted (raw) manual pages to also be installed, but in the man manual directories. For example, with confINSTALL_RAWMAN defined:

% ./Build install 
Configuration: pfx=, os=SunOS, rel=4.1.4, rbase=4, rroot=4.1, arch=sun4, sfx=
Making in ../obj.SunOS.4.1.4.sun4/sendmail
...
install -c -o bin -g bin -m 444 sendmail.0 /usr/man/cat8/sendmail.8
install -c -o bin -g bin -m 444 sendmail.8 /usr/man/man8/sendmail.8
...    etc.

But with the confINSTALL_RAWMAN not defined:

% ./Build install 
Configuration: pfx=, os=SunOS, rel=4.1.4, rbase=4, rroot=4.1, arch=sun4, sfx=
Making in ../obj.SunOS.4.1.4.sun4/sendmail
...
install -c -o bin -g bin -m 444 sendmail.0 /usr/man/cat8/sendmail.8
...    etc.