FEATURE: add indication if incoming email attachment was rejected and inform sender about it (#6376)

* FEATURE: add indication if incoming email attachment was rejected and inform sender about it

* include errors for rejected attachments in email

* don't send warning email to staged users

* use user object instead of user_id in add_attachments method

spec/components/email/receiver_spec.rb

@@ -465,10 +465,24 @@ describe Email::Receiver do
       SiteSetting.authorized_extensions = "txt"
       expect { process(:attached_txt_file) }.to change { topic.posts.count }
       expect(topic.posts.last.raw).to match(/text\.txt/)
+    end
 
-      SiteSetting.authorized_extensions = "csv"
-      expect { process(:attached_txt_file_2) }.to change { topic.posts.count }
-      expect(topic.posts.last.raw).to_not match(/text\.txt/)
+    context "when attachment is rejected" do
+      it "sends out the warning email" do
+        expect { process(:attached_txt_file) }.to change { EmailLog.count }.by(1)
+        expect(EmailLog.last.email_type).to eq("email_reject_attachment")
+      end
+
+      it "doesn't send out the warning email if sender is staged user" do
+        user.update_columns(staged: true)
+        expect { process(:attached_txt_file) }.not_to change { EmailLog.count }
+      end
+
+      it "creates the post with attachment missing message" do
+        missing_attachment_regex = Regexp.escape(I18n.t('emails.incoming.missing_attachment', filename: "text.txt"))
+        expect { process(:attached_txt_file) }.to change { topic.posts.count }
+        expect(topic.posts.last.raw).to match(/#{missing_attachment_regex}/)
+      end
     end
 
     it "supports emails with just an attachment" do