http 429 responses should suppress bounce messages to reduce email volume in rate limiting situations

app/jobs/unqueue_message_job.rb

@@ -54,7 +54,7 @@ class UnqueueMessageJob < Postal::Job
             if queued_message.attempts >= Postal.config.general.maximum_delivery_attempts
               details = "Maximum number of delivery attempts (#{queued_message.attempts}) has been reached."
               if queued_message.message.scope == 'incoming'
-                # Send bounceds to incoming e-mails when they are hard failed
+                # Send bounces to incoming e-mails when they are hard failed
                 if bounce_id = queued_message.send_bounce
                   details += " Bounce sent to sender (see message <msg:#{bounce_id}>)"
                 end
@@ -240,7 +240,10 @@ class UnqueueMessageJob < Postal::Job
 
                 # Log the result
                 log_details = result.details
-                if result.type =='HardFail' && queued_message.message.send_bounces?
+                if result.type =='HardFail' && result.suppress_bounce
+                  # The delivery hard failed, but requested that no bounce be sent
+                  log "#{log_prefix} Suppressing bounce message after hard fail"
+                elsif result.type =='HardFail' && queued_message.message.send_bounces?
                   # If the message is a hard fail, send a bounce message for this message.
                   log "#{log_prefix} Sending a bounce because message hard failed"
                   if bounce_id = queued_message.send_bounce

lib/postal/http_sender.rb

@@ -43,6 +43,10 @@ module Postal
         result.type = 'SoftFail'
         result.retry = true
         result.connect_error = true
+      elsif response[:code] == 429
+        # Rate limit exceeded, treat as a hard fail and don't send bounces
+        result.type = 'HardFail'
+        result.suppress_bounce = true
       else
         # This is permanent. Any other error isn't cool with us.
         result.type = 'HardFail'

lib/postal/send_result.rb

@@ -8,5 +8,6 @@ module Postal
     attr_accessor :connect_error
     attr_accessor :log_id
     attr_accessor :time
+    attr_accessor :suppress_bounce
   end
 end