FEATURE: accept incoming email with reply_key mismatch when original email was forwarded

lib/email/receiver.rb

@@ -429,7 +429,7 @@ module Email
       when :reply
         email_log = destination[:obj]
 
-        if email_log.user_id != user.id
+        if email_log.user_id != user.id && !forwareded_reply_key?(email_log, user)
           raise ReplyUserNotMatchingError, "email_log.user_id => #{email_log.user_id.inspect}, user.id => #{user.id.inspect}"
         end
 
@@ -442,6 +442,40 @@ module Email
       end
     end
 
+    def forwareded_reply_key?(email_log, user)
+      incoming_emails = IncomingEmail
+        .joins(:post)
+        .where('posts.topic_id = ?', email_log.topic_id)
+        .where('incoming_emails.to_addresses ILIKE :email OR incoming_emails.cc_addresses ILIKE :email', email: "%#{email_log.reply_key}%")
+        .where('incoming_emails.to_addresses ILIKE :email OR incoming_emails.cc_addresses ILIKE :email', email: "%#{user.email}%")
+
+      incoming_emails.each do |email|
+        next unless contains_email_address?(email.to_addresses, user.email) ||
+          contains_email_address?(email.cc_addresses, user.email)
+
+        return true if contains_reply_by_email_address(email.to_addresses, email_log.reply_key) ||
+          contains_reply_by_email_address(email.cc_addresses, email_log.reply_key)
+      end
+
+      false
+    end
+
+    def contains_email_address?(addresses, email)
+      return false if addresses.blank?
+      addresses.split(";").include?(email)
+    end
+
+    def contains_reply_by_email_address(addresses, reply_key)
+      return false if addresses.blank?
+
+      addresses.split(";").each do |address|
+        match = Email::Receiver.reply_by_email_address_regex.match(address)
+        return true if match && match.captures&.include?(reply_key)
+      end
+
+      false
+    end
+
     def has_been_forwarded?
       subject[/^[[:blank:]]*(fwd?|tr)[[:blank:]]?:/i] && embedded_email_raw.present?
     end

spec/components/email/receiver_spec.rb

@@ -397,7 +397,29 @@ describe Email::Receiver do
     end
 
     it "accepts emails with wrong reply key if the system knows about the forwareded email" do
+      Fabricate(:incoming_email,
+                raw: <<~RAW,
+                          Return-Path: <discourse@bar.com>
+                          From: Alice <discourse@bar.com>
+                          To: dave@bar.com, reply+4f97315cc828096c9cb34c6f1a0d6fe8@bar.com
+                          CC: carol@bar.com, bob@bar.com
+                          Subject: Hello world
+                          Date: Fri, 15 Jan 2016 00:12:43 +0100
+                          Message-ID: <10@foo.bar.mail>
+                          Mime-Version: 1.0
+                          Content-Type: text/plain; charset=UTF-8
+                          Content-Transfer-Encoding: quoted-printable
 
+                          This post was created by email.
+                RAW
+                from_address: "discourse@bar.com",
+                to_addresses: "dave@bar.com;reply+4f97315cc828096c9cb34c6f1a0d6fe8@bar.com",
+                cc_addresses: "carol@bar.com;bob@bar.com",
+                topic: topic,
+                post: post,
+                user: user)
+
+      expect { process(:reply_user_not_matching_but_known) }.to change { topic.posts.count }
     end
   end
 

spec/fixtures/emails/reply_user_not_matching_but_known.eml

@@ -0,0 +1,11 @@
+Return-Path: <bob@bar.com>
+From: Bob <bob@bar.com>
+To: reply+4f97315cc828096c9cb34c6f1a0d6fe8@bar.com
+CC: Alice <discourse@bar.com>, carol@bar.com
+Date: Fri, 15 Jan 2016 02:12:43 +0100
+Message-ID: <11@foo.bar.mail>
+Mime-Version: 1.0
+Content-Type: text/plain
+Content-Transfer-Encoding: 7bit
+
+Lorem ipsum dolor sit amet, consectetur adipiscing elit.