Add simply bounce handling

Bouncing is not an exceptional state, so let's not use exceptions to deal with it.

lib/action_mailroom/mailbox.rb

@@ -8,7 +8,7 @@ class ActionMailroom::Mailbox
   include Callbacks, Routing
 
   attr_reader :inbound_email
-  delegate :mail, to: :inbound_email
+  delegate :mail, :bounced!, to: :inbound_email
 
   def self.receive(inbound_email)
     new(inbound_email).perform_processing
@@ -37,7 +37,7 @@ class ActionMailroom::Mailbox
     def track_status_of_inbound_email
       inbound_email.processing!
       yield
-      inbound_email.delivered!
+      inbound_email.delivered! unless inbound_email.bounced?
     rescue => exception
       inbound_email.failed!
       raise

test/unit/mailbox/state_test.rb

@@ -14,6 +14,14 @@ class UnsuccessfulMailbox < ActionMailroom::Mailbox
   end
 end
 
+class BouncingMailbox < ActionMailroom::Mailbox
+  def process
+    $processed = :bounced
+    bounced!    
+  end
+end
+
+
 class ActionMailroom::Mailbox::StateTest < ActiveSupport::TestCase
   setup do
     $processed = false
@@ -32,4 +40,10 @@ class ActionMailroom::Mailbox::StateTest < ActiveSupport::TestCase
     assert @inbound_email.failed?
     assert_equal :failure, $processed
   end
+
+  test "bounced inbound emails are not delivered" do
+    BouncingMailbox.receive @inbound_email
+    assert @inbound_email.bounced?
+    assert_equal :bounced, $processed
+  end
 end