updated example to drop mail

Lua-Examples.md

@@ -39,15 +39,17 @@ end
 
 This event fires after Inbucket has accepted a message, but before it has been stored.
 
-Changes the destination mailbox to `test` for two specific recipients.
+Changes the destination mailbox to `test` from `swaks`, and does not store mail for
+`alternate`.
 
 ```lua
 local logger = require("logger")
 
 -- Original mailbox name on left, new on right.
+-- `false` causes mail for that box to be discarded.
 local mailbox_mapping = {
   ["swaks"] = "test",
-  ["james-test"] = "test",
+  ["alternate"] = false,
 }
 
 function inbucket.before.message_stored(msg)
@@ -60,17 +62,22 @@ function inbucket.before.message_stored(msg)
     local new_box = mailbox_mapping[orig_box]
     if new_box then
       logger.info(string.format("Mapping mailbox %q to %q", orig_box, new_box), {})
-      new_mailboxes[index] = new_box
+      new_mailboxes[#new_mailboxes+1] = new_box
+      made_changes = true
+    elseif new_box == false then
+      logger.info(string.format("Discarding mail for %q", orig_box), {})
       made_changes = true
     else
       -- No match, continue using the original value for this mailbox.
-      new_mailboxes[index] = orig_box
+      new_mailboxes[#new_mailboxes+1] = orig_box
     end
   end
 
   if made_changes then
     -- Recipient mailbox list was changed, return updated msg.
-    logger.info(string.format("New mailboxes: %s", table.concat(new_mailboxes, ", ")), {})
+    logger.info(
+      string.format("New mailboxes: %s", table.concat(new_mailboxes, ", ")),
+      {count = #new_mailboxes})
     msg.mailboxes = new_mailboxes
     return msg
   end