If the -D or -P option is not given in the command line, this printing method is the default method, unless the prolog.ps file is present in either of the/usr/openwin/lib/locale/$LANG/print or /usr/lib/lp/locale/$LANG/mp directories. The prolog.ps file forces mp to print using PostScript embedded fonts in the file. Even if a prolog.ps exists in a locale, using the -M option ignores the prolog.ps file and uses an mp.conf file instead, if one exists.
This method uses the /usr/lib/lp/locale/$LANG/mp/mp.conf font configuration file. You probably do not need to change this file unless you need to print using alternate fonts. This file can be configured with TrueType, Type 1, or .pcf fonts.