Configure script from port mail/kbiff has following twice and incorrect ssl check between line 25470 and line 25505:

# Check whether --enable-ssl or --disable-ssl was given.
if test "${enable_ssl+set}" = set; then
  enableval="$enable_ssl"
  use_ssl=$enableval
else
  use_ssl=yes
fi;

if test "$use_ssl" == "yes"; then

cat >>confdefs.h <<\_ACEOF
#define USE_SSL
_ACEOF

fi


# Check whether --enable-ssl or --disable-ssl was given.
if test "${enable_ssl+set}" = set; then
  enableval="$enable_ssl"
  use_ssl=$enableval
else
  use_ssl=yes
fi;

if test "$use_ssl" == "yes"; then

cat >>confdefs.h <<\_ACEOF
#define USE_SSL
_ACEOF

fi


The syntax error is in following code:
if test "$use_ssl" == "yes"; then

String comparsion with test only needs one equals sign.

Fix: 

Remove twice code and change line 
    if test "$use_ssl" == "yes"; then
to
    if test "$use_ssl" = "yes"; then