FIX: use MD5 of the email_string when there's no 'Message-Id'

app/jobs/scheduled/poll_mailbox.rb

@@ -40,7 +40,6 @@ module Jobs
       message_template = case e
         when Email::Receiver::EmptyEmailError             then :email_reject_empty
         when Email::Receiver::NoBodyDetectedError         then :email_reject_empty
-        when Email::Receiver::NoMessageIdError            then :email_reject_no_message_id
         when Email::Receiver::AutoGeneratedEmailError     then :email_reject_auto_generated
         when Email::Receiver::InactiveUserError           then :email_reject_inactive_user
         when Email::Receiver::BlockedUserError            then :email_reject_blocked_user

config/locales/server.en.yml

@@ -1837,13 +1837,6 @@ en:
 
         Your reply was sent from a different email address than the one we expected, so we're not sure if this is the same person. Try sending from another email address, or contact a staff member.
 
-    email_reject_no_message_id:
-      subject_template: "[%{site_name}] Email issue -- No Message Id"
-      text_body_template: |
-        We're sorry, but your email message to %{destination} (titled %{former_title}) didn't work.
-
-        We couldn't find a `Message-Id` header in the email. Try sending from a different email address, or contact a staff member.
-
     email_reject_no_account:
       subject_template: "[%{site_name}] Email issue -- Unknown Account"
       text_body_template: |

lib/email/receiver.rb

@@ -1,3 +1,4 @@
+require "digest"
 require_dependency "new_post_manager"
 require_dependency "post_action_creator"
 require_dependency "email/html_cleaner"
@@ -9,7 +10,6 @@ module Email
 
     class ProcessingError             < StandardError; end
     class EmptyEmailError             < ProcessingError; end
-    class NoMessageIdError            < ProcessingError; end
     class AutoGeneratedEmailError     < ProcessingError; end
     class NoBodyDetectedError         < ProcessingError; end
     class InactiveUserError           < ProcessingError; end
@@ -29,7 +29,7 @@ module Email
       raise EmptyEmailError if mail_string.blank?
       @raw_email = mail_string
       @mail = Mail.new(@raw_email)
-      raise NoMessageIdError if @mail.message_id.blank?
+      @message_id = @mail.message_id.presence || Digest::MD5.hexdigest(mail_string)
     end
 
     def process!
@@ -42,7 +42,7 @@ module Email
     end
 
     def find_or_create_incoming_email
-      IncomingEmail.find_or_create_by(message_id: @mail.message_id) do |ie|
+      IncomingEmail.find_or_create_by(message_id: @message_id) do |ie|
         ie.raw = @raw_email
         ie.subject = subject
         ie.from_address = @from_email

spec/components/email/receiver_spec.rb

@@ -21,14 +21,6 @@ describe Email::Receiver do
     expect { Email::Receiver.new("") }.to raise_error(Email::Receiver::EmptyEmailError)
   end
 
-  it "raises an NoMessageIdError when 'mail_string' is not an email" do
-    expect { Email::Receiver.new("wat") }.to raise_error(Email::Receiver::NoMessageIdError)
-  end
-
-  it "raises an NoMessageIdError when 'mail_string' is missing the message_id" do
-    expect { Email::Receiver.new(email(:missing_message_id)) }.to raise_error(Email::Receiver::NoMessageIdError)
-  end
-
   it "raises an AutoGeneratedEmailError when the mail is auto generated" do
     expect { process(:auto_generated_precedence) }.to raise_error(Email::Receiver::AutoGeneratedEmailError)
     expect { process(:auto_generated_header) }.to raise_error(Email::Receiver::AutoGeneratedEmailError)
@@ -65,6 +57,12 @@ describe Email::Receiver do
     let(:post) { create_post(topic: topic, user: user) }
     let!(:email_log) { Fabricate(:email_log, reply_key: reply_key, user: user, topic: topic, post: post) }
 
+    it "uses MD5 of 'mail_string' there is no message_id" do
+      mail_string = email(:missing_message_id)
+      expect { Email::Receiver.new(mail_string).process! }.to change { IncomingEmail.count }
+      expect(IncomingEmail.last.message_id).to eq(Digest::MD5.hexdigest(mail_string))
+    end
+
     it "raises a ReplyUserNotMatchingError when the email address isn't matching the one we sent the notification to" do
       expect { process(:reply_user_not_matching) }.to raise_error(Email::Receiver::ReplyUserNotMatchingError)
     end

spec/fixtures/emails/missing_message_id.eml

@@ -1,5 +1,8 @@
-From: Foo Bar <foo@bar.com>
+From: Foo Bar <discourse@bar.com>
+To: reply+4f97315cc828096c9cb34c6f1a0d6fe8@bar.com
 Date: Fri, 15 Jan 2016 00:12:43 +0100
 Mime-Version: 1.0
 Content-Type: text/plain
 Content-Transfer-Encoding: 7bit
+
+Some body