Implement postmark conversion from 'OriginalRecipient' to 'X-Original-To'

actionmailbox/app/controllers/action_mailbox/ingresses/postmark/inbound_emails_controller.rb

@@ -49,7 +49,7 @@ module ActionMailbox
     param_encoding :create, "RawEmail", Encoding::ASCII_8BIT
 
     def create
-      ActionMailbox::InboundEmail.create_and_extract_message_id! params.require("RawEmail")
+      ActionMailbox::InboundEmail.create_and_extract_message_id! mail
     rescue ActionController::ParameterMissing => error
       logger.error <<~MESSAGE
         #{error.message}
@@ -59,5 +59,12 @@ module ActionMailbox
       MESSAGE
       head :unprocessable_entity
     end
+
+    private
+      def mail
+        params.require("RawEmail").tap do |raw_email|
+          raw_email.prepend("X-Original-To: ", params.require("OriginalRecipient"), "\n") if params.key?("OriginalRecipient")
+        end
+      end
   end
 end

actionmailbox/test/controllers/ingresses/postmark/inbound_emails_controller_test.rb

@@ -31,6 +31,22 @@ class ActionMailbox::Ingresses::Postmark::InboundEmailsControllerTest < ActionDi
     assert_equal "05988AA6EC0D44318855A5E39E3B6F9E@jansterba.com", inbound_email.message_id
   end
 
+  test "add X-Original-To to email from Postmark" do
+    assert_difference -> { ActionMailbox::InboundEmail.count }, +1 do
+      post rails_postmark_inbound_emails_url,
+        headers: { authorization: credentials }, params: {
+          RawEmail: file_fixture("../files/welcome.eml").read,
+          OriginalRecipient: "thisguy@domain.abcd",
+        }
+    end
+
+    assert_response :no_content
+
+    inbound_email = ActionMailbox::InboundEmail.last
+    mail = Mail.from_source(inbound_email.raw_email.download)
+    assert_equal "thisguy@domain.abcd", mail.header["X-Original-To"].decoded
+  end
+
   test "rejecting when RawEmail param is missing" do
     assert_no_difference -> { ActionMailbox::InboundEmail.count } do
       post rails_postmark_inbound_emails_url,