Port is mail/qmail-ldap, with versions from Makefile like:

  PORTNAME=	qmail
  PORTVERSION=	${QMAIL_VERSION}.${LDAP_PATCH_DATE}
  CATEGORIES=	mail
  PKGNAMESUFFIX=	-ldap

  PATCH_SITES=	http://www.nrg4u.com/qmail/:ldap
  PATCHFILES=	qmail-ldap-1.03-${LDAP_PATCH_DATE}.patch.gz:ldap
  PATCH_DIST_STRIP+=	-p1
  LDAP_PATCH_DATE=	20020901

Build port with flags to turn on CLEARTEXTPASSWD (which I need),
invoked like:

  make -D WITH_LDAP2 -D WITHOUT_LDAP_CLUSTER WITH_LDAP_DEBUG=yes  WITH_CLEARTEXTPASSWD=yes WITH_DASH_EXT=yes 

The Makefile invokes perl to edit the qmail work/qmail-1.03/Makefile:

  .if defined(WITH_CLEARTEXTPASSWD)
	  @${PERL} -pi -ne "s|# -DCLEARTEXTPASSWD to the LDAPFLAGS|LDAPFLAGS\+=-DCLEARTEXTPASSWD|" \
		  ${WRKSRC}/Makefile
  .endif # WITH_CLEARTEXTPASSWD

But the work/qmail-1.03/Makefile line is:

  # -DCLEARTEXTPASSWD to use cleartext passwords (a bad idea on production
  # systems)

So the port Makefile edit fails and CLEARTEXTPASSWD is NOT set.

Fix: 

Change the perl edit to match the current qmail-ldap patch Makefile text.

Would probably be wise to upgrade this port to a modern version of
qmail-ldap patch too.
How-To-Repeat: 
As above "make" invocations.