FIX: Ensure group SMTP and message builder always uses from address for Reply-To when IMAP is enabled (#11037)

There is a site setting reply_by_email_enabled which when combined with reply_by_email_address creates a Reply-To header in emails in the format "test+%{reply_key}@test.com" along with a PostReplyKey record, so when replying Discourse knows where to route the reply.

However this conflicts with the IMAP implementation. Since we are sending the email for a group via SMTP and from their actual email account, we want all replys to go to that email account as well so the IMAP sync job can pick them up and put them in the correct place. So if the group has IMAP enabled and configured, then the reply-to header will be correct.

This PR also makes a further fix to 64b0b50 by using the correct recipient user for the PostReplyKey record. If the post user is used we encounter this error:

if destination.user_id != user.id && !forwarded_reply_key?(destination, user)
  raise ReplyUserNotMatchingError, "post_reply_key.user_id => #{destination.user_id.inspect}, user.id => #{user.id.inspect}"
end
This is because the user above is found from the from_address, but the destination which is the PostReplyKey is made by the post.user, which will be different people.

app/jobs/regular/group_smtp_email.rb

@@ -10,10 +10,11 @@ module Jobs
       group = Group.find_by(id: args[:group_id])
       post = Post.find_by(id: args[:post_id])
       email = args[:email]
+      recipient_user = ::UserEmail.find_by(email: email, primary: true)&.user
 
       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, post.user).send
+      Email::Sender.new(message, :group_smtp, recipient_user).send
 
       # Create an incoming email record to avoid importing again from IMAP
       # server.

app/mailers/group_smtp_mailer.rb

@@ -48,6 +48,7 @@ class GroupSmtpMailer < ActionMailer::Base
       group_name: from_group.name,
       allow_reply_by_email: true,
       only_reply_by_email: true,
+      use_from_address_for_reply_to: from_group.imap_enabled?,
       private_reply: post.topic.private_message?,
       participants: participants(post),
       include_respond_instructions: true,

app/models/group.rb

@@ -817,6 +817,11 @@ class Group < ActiveRecord::Base
     }
   end
 
+  def imap_enabled?
+    return false if !SiteSetting.enable_imap
+    imap_config.values.compact.length == imap_config.keys.length
+  end
+
   def email_username_regex
     user, domain = email_username.split('@')
     if user.present? && domain.present?

lib/email/message_builder.rb

@@ -153,7 +153,7 @@ module Email
       # please, don't send us automatic responses...
       result['X-Auto-Response-Suppress'] = 'All'
 
-      if allow_reply_by_email?
+      if allow_reply_by_email? && !@opts[:use_from_address_for_reply_to]
         result[ALLOW_REPLY_BY_EMAIL_HEADER] = true
         result['Reply-To'] = reply_by_email_address
       else

spec/jobs/regular/group_smtp_email_spec.rb

@@ -5,6 +5,7 @@ require 'rails_helper'
 RSpec.describe Jobs::GroupSmtpEmail do
   let(:post) { Fabricate(:post) }
   let(:group) { Fabricate(:imap_group) }
+  let!(:recipient_user) { Fabricate(:user, email: "test@test.com") }
   let(:args) do
     {
       group_id: group.id,
@@ -23,7 +24,7 @@ RSpec.describe Jobs::GroupSmtpEmail do
   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))
+    Email::Sender.expects(:new).with(message, :group_smtp, recipient_user).returns(stub(send: nil))
     subject.execute(args)
   end
 
@@ -37,7 +38,7 @@ RSpec.describe Jobs::GroupSmtpEmail do
   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
+    post_reply_key = PostReplyKey.where(user_id: recipient_user, 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

spec/mailers/group_smtp_mailer_spec.rb

@@ -56,6 +56,7 @@ describe GroupSmtpMailer do
 
   before do
     SiteSetting.enable_smtp = true
+    SiteSetting.enable_imap = true
     Jobs.run_immediately!
   end
 
@@ -69,8 +70,49 @@ describe GroupSmtpMailer do
 
     sent_mail = ActionMailer::Base.deliveries[0]
     expect(sent_mail.to).to contain_exactly('john@doe.com')
+    expect(sent_mail.reply_to).to contain_exactly('bugs@gmail.com')
     expect(sent_mail.subject).to eq('Re: Hello from John')
     expect(sent_mail.to_s).to include(raw)
   end
 
+  context "when the site has a reply by email address configured" do
+    before do
+      SiteSetting.manual_polling_enabled = true
+      SiteSetting.reply_by_email_address = "test+%{reply_key}@test.com"
+      SiteSetting.reply_by_email_enabled = true
+    end
+
+    it 'uses the correct IMAP/SMTP reply to address' do
+      post = PostCreator.create(user,
+                                topic_id: receiver.incoming_email.topic.id,
+                                raw: raw
+                               )
+
+      expect(ActionMailer::Base.deliveries.size).to eq(1)
+
+      sent_mail = ActionMailer::Base.deliveries[0]
+      expect(sent_mail.reply_to).to contain_exactly('bugs@gmail.com')
+    end
+
+    context "when IMAP is disabled for the group" do
+      before do
+        group.update(
+          imap_server: nil
+        )
+      end
+
+      it "uses the reply key based reply to address" do
+        post = PostCreator.create(user,
+                                  topic_id: receiver.incoming_email.topic.id,
+                                  raw: raw
+                                 )
+
+        expect(ActionMailer::Base.deliveries.size).to eq(1)
+
+        sent_mail = ActionMailer::Base.deliveries[0]
+        post_reply_key = PostReplyKey.last
+        expect(sent_mail.reply_to).to contain_exactly("test+#{post_reply_key.reply_key}@test.com")
+      end
+    end
+  end
 end

spec/models/group_spec.rb

@@ -973,7 +973,7 @@ describe Group do
     end
   end
 
-  describe "#imap_mailboxes" do
+  describe "IMAP" do
     let(:group) { Fabricate(:group) }
 
     def mock_imap
@@ -1010,6 +1010,21 @@ describe Group do
       Discourse.redis.del("group_imap_mailboxes_#{group.id}")
     end
 
+    describe "#imap_enabled?" do
+      it "returns true if imap is configured and enabled for the site" do
+        mock_imap
+        configure_imap
+        enable_imap
+        expect(group.imap_enabled?).to eq(true)
+      end
+
+      it "returns false if imap is configured and not enabled for the site" do
+        configure_imap
+        expect(group.imap_enabled?).to eq(false)
+      end
+    end
+
+    describe "#imap_mailboxes" do
       it "returns an empty array if group imap is not configured" do
         expect(group.imap_mailboxes).to eq([])
       end
@@ -1045,6 +1060,7 @@ describe Group do
         group.imap_mailboxes
       end
     end
+  end
 
   context "Unicode usernames and group names" do
     before { SiteSetting.unicode_usernames = true }