-# Since most operating systems do not include a crypt16() function (yet?), Exim
-# has one of its own, which it uses unless HAVE_CRYPT16 is defined. Normally,
-# that will be set in an OS-specific Makefile for the OS that have such a
-# function, so you should not need to bother with it.
+# Some operating systems do not include a crypt16() function, so Exim has one
+# of its own, which it uses unless HAVE_CRYPT16 is defined. Normally, that will
+# be set in an OS-specific Makefile for the OS that have such a function, so
+# you should not need to bother with it.
+
+# *** WARNING *** WARNING *** WARNING *** WARNING *** WARNING ***
+# It turns out that the above is not entirely accurate. As well as crypt16()
+# there is a function called bigcrypt() that some operating systems have. This
+# may or may not use the same algorithm, and both of them may be different to
+# Exim's built-in crypt16() that is used unless HAVE_CRYPT16 is defined.
+#
+# However, since there is now a move away from the traditional crypt()
+# functions towards using SHA1 and other algorithms, tidying up this area of
+# Exim is seen as very low priority. In practice, if you need to, you can
+# define DEFAULT_CRYPT to the name of any function that has the same interface
+# as the traditional crypt() function.
+# *** WARNING *** WARNING *** WARNING *** WARNING *** WARNING ***