FIX: Prioritize VERP key over final_recipient header in bounced email

Per RFC3464 2.3.2, the final_recipient header may not match the address we originally sent the email to.

lib/email/receiver.rb

@@ -513,13 +513,13 @@ module Email
     def parse_from_field(mail = nil)
       mail ||= @mail
 
-      if mail.bounced?
+      if email_log.present?
+        email = email_log.to_address || email_log.user&.email
+        return [email, email_log.user&.username]
+      elsif mail.bounced?
         Array.wrap(mail.final_recipient).each do |from|
           return extract_from_address_and_name(from)
         end
-      elsif email_log.present?
-        email = email_log.user&.email || email_log.to_address
-        return [email, email_log.user&.username]
       end
 
       return unless mail[:from]

spec/components/email/receiver_spec.rb

@@ -212,6 +212,14 @@ describe Email::Receiver do
       expect(email_log_2.bounced).to eq(true)
     end
 
+    it "works when the final recipient is different" do
+      expect { process(:verp_bounce_different_final_recipient) }.to raise_error(Email::Receiver::BouncedEmailError)
+
+      email_log.reload
+      expect(email_log.bounced).to eq(true)
+      expect(email_log.user.user_stat.bounce_score).to eq(SiteSetting.soft_bounce_score)
+    end
+
     it "sends a system message once they reach the 'bounce_score_threshold'" do
       expect(user.active).to eq(true)
 

spec/fixtures/emails/verp_bounce_different_final_recipient.eml

@@ -0,0 +1,39 @@
+Delivered-To: foo+verp-14b08c855160d67f2e0c2f8ef36e251e@discourse.org
+Date: Thu,  7 Apr 2016 19:04:30 +0900 (JST)
+From: MAILER-DAEMON@b-s-c.co.jp (Mail Delivery System)
+Subject: Undelivered Mail Returned to Sender
+To: foo+verp-14b08c855160d67f2e0c2f8ef36e251e@discourse.org
+MIME-Version: 1.0
+Content-Type: multipart/report; report-type=delivery-status;
+    boundary="18F5D18A0075.1460023470/some@daemon.com"
+
+This is a MIME-encapsulated message.
+
+--18F5D18A0075.1460023470/some@daemon.com
+Content-Description: Notification
+Content-Type: text/plain; charset=us-ascii
+
+Your email bounced
+
+--18F5D18A0075.1460023470/some@daemon.com
+Content-Description: Delivery report
+Content-Type: message/delivery-status
+
+Final-Recipient: rfc822; catchall@b-s-c.co.jp
+Original-Recipient: rfc822;linux-admin@b-s-c.co.jp
+Action: failed
+Status: 4.1.1
+Diagnostic-Code: X-Postfix; unknown user: "linux-admin"
+
+--18F5D18A0075.1460023470/some@daemon.com
+Content-Description: Undelivered Message
+Content-Type: message/rfc822
+
+Return-Path: <foo+verp-14b08c855160d67f2e0c2f8ef36e251e@discourse.org>
+Date: Thu, 07 Apr 2016 03:04:28 -0700 (PDT)
+From: foo+verp-14b08c855160d67f2e0c2f8ef36e251e@discourse.org
+X-Discourse-Auto-Generated: marked
+
+This is the body
+
+--18F5D18A0075.1460023470/some@daemon.com--