FIX: Prevent resurrecting old topics via email reply for group inboxes with SMTP enabled (#13382)

We already reject email replies to public topics via `SiteSetting.disallow_reply_by_email_after_days` and raising the `OldDestinationError`. This PR introduces similar behaviour for group inboxes, but without the rejection, and **only when SMTP is enabled for the group**.

If a reply is sent via email and the post is older than `SiteSetting.disallow_reply_by_email_after_days` days ago, then we create a new topic instead of making a reply in the old one and link back to the original topic. This is done to prevent long running group inbox discussions.

spec/components/email/receiver_spec.rb

@@ -986,8 +986,14 @@ describe Email::Receiver do
     end
 
     context "emailing a group by email_username and following reply flow" do
-      let!(:topic) do
-        group.update!(email_username: "team@somesmtpaddress.com")
+      let!(:original_inbound_email_topic) do
+        group.update!(
+          email_username: "team@somesmtpaddress.com",
+          smtp_server: "smtp.test.com",
+          smtp_port: 587,
+          smtp_ssl: true,
+          smtp_enabled: true
+        )
         process(:email_to_group_email_username_1)
         Topic.last
       end
@@ -999,6 +1005,7 @@ describe Email::Receiver do
 
       before do
         NotificationEmailer.enable
+        SiteSetting.disallow_reply_by_email_after_days = 10000
         Jobs.run_immediately!
       end
 
@@ -1006,17 +1013,17 @@ describe Email::Receiver do
         group_post = PostCreator.create(
           user_in_group,
           raw: "Thanks for your request. Please try to restart.",
-          topic_id: topic.id
+          topic_id: original_inbound_email_topic.id
         )
         email_log = EmailLog.last
         [email_log, group_post]
       end
 
       it "the inbound processed email creates an incoming email and topic record correctly, and adds the group to the topic" do
-        incoming = IncomingEmail.find_by(topic: topic)
+        incoming = IncomingEmail.find_by(topic: original_inbound_email_topic)
         user = User.find_by_email("two@foo.com")
-        expect(topic.topic_allowed_users.first.user_id).to eq(user.id)
-        expect(topic.topic_allowed_groups.first.group_id).to eq(group.id)
+        expect(original_inbound_email_topic.topic_allowed_users.first.user_id).to eq(user.id)
+        expect(original_inbound_email_topic.topic_allowed_groups.first.group_id).to eq(group.id)
         expect(incoming.to_addresses).to eq("team@somesmtpaddress.com")
         expect(incoming.from_address).to eq("two@foo.com")
         expect(incoming.message_id).to eq("u4w8c9r4y984yh98r3h69873@foo.bar.mail")
@@ -1024,7 +1031,7 @@ describe Email::Receiver do
 
       it "creates an EmailLog when someone from the group replies, and does not create an IncomingEmail record for the reply" do
         email_log, group_post = reply_as_group_user
-        expect(email_log.message_id).to eq("topic/#{topic.id}/#{group_post.id}@test.localhost")
+        expect(email_log.message_id).to eq("topic/#{original_inbound_email_topic.id}/#{group_post.id}@test.localhost")
         expect(email_log.to_address).to eq("two@foo.com")
         expect(email_log.email_type).to eq("user_private_message")
         expect(email_log.post_id).to eq(group_post.id)
@@ -1056,7 +1063,7 @@ describe Email::Receiver do
         end.to change { Topic.count }.by(1).and change { Post.count }.by(1)
 
         reply_post = Post.last
-        expect(reply_post.topic_id).not_to eq(topic.id)
+        expect(reply_post.topic_id).not_to eq(original_inbound_email_topic.id)
       end
 
       it "processes the reply from the user as a reply if they have replied from a different address (e.g. auto forward) and allow_unknown_sender_topic_replies is enabled" do
@@ -1070,7 +1077,32 @@ describe Email::Receiver do
         end.to change { Topic.count }.by(0).and change { Post.count }.by(1)
 
         reply_post = Post.last
-        expect(reply_post.topic_id).to eq(topic.id)
+        expect(reply_post.topic_id).to eq(original_inbound_email_topic.id)
+      end
+
+      it "creates a new topic with a reference back to the original if replying to a too old topic" do
+        SiteSetting.disallow_reply_by_email_after_days = 2
+        email_log, group_post = reply_as_group_user
+
+        group_post.update(created_at: 10.days.ago)
+        group_post.topic.update(created_at: 10.days.ago)
+
+        reply_email = email(:email_to_group_email_username_2)
+        reply_email.gsub!("MESSAGE_ID_REPLY_TO", email_log.message_id)
+        expect do
+          Email::Receiver.new(reply_email).process!
+        end.to change { Topic.count }.by(1).and change { Post.count }.by(1)
+
+        reply_post = Post.last
+        new_topic = Topic.last
+
+        expect(reply_post.topic).to eq(new_topic)
+        expect(reply_post.raw).to include(
+          I18n.t(
+            "emails.incoming.continuing_old_discussion",
+            url: group_post.topic.url, title: group_post.topic.title, count: SiteSetting.disallow_reply_by_email_after_days
+          )
+        )
       end
     end