FIX: Pass user to Email::Sender to avoid broken reply key for group_smtp email (#10978)

Our Email::Sender class accepts an optional user argument, which is used to create a PostReplyKey record when present. This record is used to sub out the %{reply_key} placeholder in the Reply-To mail header, so if we do not pass in the user we get a broken Reply-To header.

This is especially problematic in the IMAP group SMTP situation, because these emails go to customers that we are replying to, and when they reply to us the email bounces! This fixes the issue by passing user to the Email::Sender when sending a group_smtp email but there is still more to do in another PR.

This Email::Sender optional user is a bit of a footgun IMO, especially because most of the time we use it there is a user we can source. I would like to do another PR for this after this one to make the parameter not optional, so we don't end up with these reply issues down the line again.

app/jobs/regular/group_smtp_email.rb

@@ -13,7 +13,7 @@ module Jobs
 
       Rails.logger.debug("[IMAP] Sending email for group #{group.name} and post #{post.id}")
       message = GroupSmtpMailer.send_mail(group, email, post)
-      Email::Sender.new(message, :group_smtp).send
+      Email::Sender.new(message, :group_smtp, post.user).send
 
       # Create an incoming email record to avoid importing again from IMAP
       # server.

lib/email/sender.rb

@@ -388,9 +388,7 @@ module Email
     end
 
     def set_reply_key(post_id, user_id)
-      return unless user_id &&
+      return if !user_id || !post_id || !header_value(Email::MessageBuilder::ALLOW_REPLY_BY_EMAIL_HEADER).present?
-        post_id &&
-        header_value(Email::MessageBuilder::ALLOW_REPLY_BY_EMAIL_HEADER).present?
 
       # use safe variant here cause we tend to see concurrency issue
       reply_key = PostReplyKey.find_or_create_by_safe!(

spec/fabricators/group_fabricator.rb

@@ -8,3 +8,17 @@ Fabricator(:public_group, from: :group) do
   public_admission true
   public_exit true
 end
+
+Fabricator(:imap_group, from: :group) do
+  smtp_server "smtp.ponyexpress.com"
+  smtp_port 587
+  smtp_ssl true
+  imap_server "imap.ponyexpress.com"
+  imap_port 993
+  imap_ssl true
+  imap_mailbox_name "All Mail"
+  imap_uid_validity 0
+  imap_last_uid 0
+  email_username "discourseteam@ponyexpress.com"
+  email_password "test"
+end

spec/jobs/regular/group_smtp_email_spec.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Jobs::GroupSmtpEmail do
+  let(:post) { Fabricate(:post) }
+  let(:group) { Fabricate(:imap_group) }
+  let(:args) do
+    {
+      group_id: group.id,
+      post_id: post.id,
+      email: "test@test.com"
+    }
+  end
+
+  before do
+    SiteSetting.reply_by_email_address = "test+%{reply_key}@incoming.com"
+    SiteSetting.manual_polling_enabled = true
+    SiteSetting.reply_by_email_enabled = true
+    SiteSetting.enable_smtp = true
+  end
+
+  it "sends an email using the GroupSmtpMailer and Email::Sender" do
+    message = Mail::Message.new(body: "hello", to: "myemail@example.invalid")
+    GroupSmtpMailer.expects(:send_mail).with(group, "test@test.com", post).returns(message)
+    Email::Sender.expects(:new).with(message, :group_smtp, post.user).returns(stub(send: nil))
+    subject.execute(args)
+  end
+
+  it "creates an IncomingEmail record to avoid double processing via IMAP" do
+    subject.execute(args)
+    incoming = IncomingEmail.find_by(post_id: post.id, user_id: post.user_id, topic_id: post.topic_id)
+    expect(incoming).not_to eq(nil)
+    expect(incoming.message_id).to eq("topic/#{post.topic_id}@test.localhost")
+  end
+
+  it "creates a PostReplyKey and correctly uses it for the email reply_key substitution" do
+    subject.execute(args)
+    incoming = IncomingEmail.find_by(post_id: post.id, user_id: post.user_id, topic_id: post.topic_id)
+    post_reply_key = PostReplyKey.where(user_id: post.user_id, post_id: post.id).first
+    expect(post_reply_key).not_to eq(nil)
+    expect(incoming.raw).to include("Reply-To: Discourse <test+#{post_reply_key.reply_key}@incoming.com>")
+  end
+end