add comment regarding UNHANDLED in maildroprc

filters/cropswap-members@shandan.one

@@ -20,7 +20,7 @@ if ($DISPATCH)
    {
       EXITCODE=$UNREGISTERED
       cc "|$DEBUGMAIL unregistered"
-      # this is not temporary error
+      # this is not a temporary error
       # and we send no response to
       # unregistered email as the
       # email address could be:

maildroprc

@@ -43,6 +43,8 @@ cc "|$DEBUGMAIL processing"
 if ($FROM eq "")
 {
    EXITCODE=$UNHANDLED
+   # this should only be able to happen
+   # when invoking maildrop on the cmdline
    exit
 }
 
@@ -106,4 +108,6 @@ else
 
 EXITCODE=$UNHANDLED
 cc "|$DEBUGMAIL unhandled"
+# this should only be able to happen
+# when invoking maildrop on the cmdline
 exit