FIX: use metadata to hold the message_id with sparkpost

app/controllers/webhooks_controller.rb

@@ -91,7 +91,7 @@ class WebhooksController < ActionController::Base
   def sparkpost
     events = params["_json"] || [params]
     events.each do |event|
-      message_id = event["msys"]["message_event"]["message_id"] rescue nil
+      message_id = event["msys"]["message_event"]["rcpt_meta"]["message_id"] rescue nil
       bounce_class = event["msys"]["message_event"]["bounce_class"] rescue nil
       next unless message_id && bounce_class
 

lib/email/sender.rb

@@ -133,12 +133,14 @@ module Email
       @message.header['X-Discourse-Post-Id']   = nil if post_id.present?
       @message.header['X-Discourse-Reply-Key'] = nil if reply_key.present?
 
-      # pass the original message_id when using mailjet/mandrill
+      # pass the original message_id when using mailjet/mandrill/sparkpost
       case ActionMailer::Base.smtp_settings[:address]
       when /\.mailjet\.com/
         @message.header['X-MJ-CustomID'] = @message.message_id
       when "smtp.mandrillapp.com"
         @message.header['X-MC-Metadata'] = { message_id: @message.message_id }.to_json
+      when "smtp.sparkpostmail.com"
+        @message.header['X-MSYS-API'] = { metadata: { message_id: @message.message_id } }.to_json
       end
 
       # Suppress images from short emails

spec/controllers/webhooks_controller_spec.rb

@@ -109,7 +109,9 @@ describe WebhooksController do
         "msys" => {
           "message_event" => {
             "bounce_class" => 10,
-            "message_id" => message_id
+            "rcpt_meta" => {
+              "message_id" => message_id
+            }
           }
         }
       }]