+.B $MHMTSCONF
+.RS 5
+If this variable is set to a non-null value, it specifies the
+name of the mail transport configuration file to use by
+.BR post ,
+.BR inc ,
+and other programs that interact with the mail transport system,
+instead of the default. See mh-tailor(5).
+.RE
+.PP
+.B $MHMTSUSERCONF
+.RS 5
+If this variable is set to a non-null value, it specifies the name of
+a mail transport configuration file to be read in addition to the
+default. See mh-tailor(5).
+.RE
+.PP
+.B $MHTMPDIR
+.B $TMPDIR
+.B $TMP
+.RS 5
+These variables are searched, in order, for the directory in which to
+create some temporary files.
+.RE
+.PP
+.B $MM_NOASK
+.RS 5
+Setting this variable is set to 1 has the same effect as specifying
+the
+.B \-nolist
+and
+.B \-nopause
+switches to
+.BR mhbuild ,
+.BR mhn ,
+and
+.BR mhshow .
+OBSOLETE: will be removed in a future version of nmh.
+.RE
+.PP
+.B $MHLDEBUG
+.RS 5
+If this variable is set to a non-null value,
+.B mhl
+will emit debugging information.
+.RE
+.PP
+.B $MHPDEBUG
+.RS 5
+If this variable is set to a non-null value,
+.B pick
+will emit a representation of the search pattern.
+.RE
+.PP
+.B $MHPOPDEBUG
+.RS 5
+If this variable is set to a non-null value,
+.B msgchck
+and
+.B inc
+will display their interaction with the POP server.
+This mechanism is obsolete; use the
+.B \-snoop
+switch instead.
+.RE
+.PP
+.B $MHWDEBUG
+.RS 5
+If this variable is set to a non-null value,
+.B nmh
+commands that use the
+.BR Alternate\-Mailboxes
+profile entry will display debugging information
+about the values in that entry.
+.RE
+.PP