Refactor RequestMailer#receive

Loop through exact matches and delivery emails to each info request.
This is now possible because we check `InfoRequest#already_received?`
when calling `InfoRequest#receive`.

Previously this could result in requests receiving an email multiple
times due to the same email coming in to the mail server multiple times,
once for each address in the `To` header.

Fixes #7913

app/mailers/request_mailer.rb

@@ -252,29 +252,31 @@ def receive(email, raw_email, source = :mailin)
     # Find exact matches for info requests
     exact_info_requests = requests_matching_email(email)
 
-    # Find any guesses for info requests
-    unless exact_info_requests.count == 1
-      guessed_info_requests = Guess.guessed_info_requests(email)
-    end
-
-    # If there is only one info request matching mail, it gets attached to the
-    # request to be archived with it
-    if exact_info_requests.count == 1 || guessed_info_requests.count == 1
-      info_request = exact_info_requests.first || guessed_info_requests.first
-
-      if exact_info_requests.empty? && guessed_info_requests.count == 1
-        info_request.log_event(
-          'redeliver_incoming',
-          editor: 'automatic',
-          destination_request: info_request
-        )
+    if exact_info_requests.count > 0
+      # Go through each exact info request and deliver the email
+      exact_info_requests.each do |info_request|
+        info_request.receive(email, raw_email, opts)
       end
 
+      return
+    end
+
+    # If there are no exact matches, find any guessed requests
+    guessed_info_requests = Guess.guessed_info_requests(email)
+
+    if guessed_info_requests.count == 1
+      # If there one guess automatically redeliver the email to that and log it
+      # as an event
+      info_request = guessed_info_requests.first
+      info_request.log_event(
+        'redeliver_incoming',
+        editor: 'automatic',
+        destination_request: info_request
+      )
       info_request.receive(email, raw_email, opts)
 
     else
-      # Otherwise, if there are no matching IRs, multiple IRs, or multiple IR
-      # guesses, we send the mail to the holding pen
+      # Otherwise we send the mail to the holding pen
       send_to_holding_pen(email, raw_email, opts)
     end
   end

spec/mailers/request_mailer_spec.rb

@@ -43,6 +43,85 @@
       deliveries.clear
     end
 
+    it "should append the email to each exact request address, unless that request has already received the email" do
+      ir = info_requests(:fancy_dog_request)
+      raw_email_data = <<~EML
+        From: EMAIL_FROM
+        To: EMAIL_TO
+        Message-ID: [email protected]
+        Subject: Basic Email
+
+        Hello, World
+      EML
+      expect(ir.incoming_messages.count).to eq(1) # in the fixture
+      receive_incoming_mail(
+        raw_email_data,
+        email_to: ir.incoming_email
+      )
+      expect(ir.incoming_messages.count).to eq(2) # one more arrives
+      # send the email again
+      receive_incoming_mail(
+        raw_email_data,
+        email_to: ir.incoming_email
+      )
+      # this shouldn't add to the number of incoming mails
+      expect(ir.incoming_messages.count).to eq(2)
+      # send an email with a new Message-ID
+      raw_email_data = <<~EML
+        From: EMAIL_FROM
+        To: EMAIL_TO
+        Message-ID: [email protected]
+        Subject: Basic Email
+
+        Hello, World
+      EML
+      receive_incoming_mail(
+        raw_email_data,
+        email_to: ir.incoming_email
+      )
+      # this should add to the number of incoming mails
+      expect(ir.incoming_messages.count).to eq(3)
+    end
+
+    it 'should append the email to every request matches, unless the requests has already received the email' do
+      info_request_1 = FactoryBot.create(:info_request)
+      info_request_2 = FactoryBot.create(:info_request)
+
+      expect(info_request_1.incoming_messages.count).to eq(0)
+      expect(info_request_2.incoming_messages.count).to eq(0)
+
+      raw_email_data = <<~EML
+        From: EMAIL_FROM
+        To: EMAIL_TO
+        Message-ID: [email protected]
+        Subject: Basic Email
+
+        Hello, World
+      EML
+
+      # send email to one request
+      receive_incoming_mail(
+        raw_email_data,
+        email_to: info_request_1.incoming_email
+      )
+
+      expect(info_request_1.incoming_messages.count).to eq(1)
+      expect(info_request_2.incoming_messages.count).to eq(0)
+
+      # send same email to both requests, should only be delivered to the
+      # request which hasn't already received the email
+      receive_incoming_mail(
+        raw_email_data,
+        email_to: [
+          info_request_1.incoming_email,
+          info_request_2.incoming_email
+        ].join(', ')
+      )
+
+      expect(info_request_1.incoming_messages.count).to eq(1)
+      expect(info_request_2.incoming_messages.count).to eq(1)
+    end
+
     it "should store mail in holding pen and send to admin when the email is not to any information request" do
       ir = info_requests(:fancy_dog_request)
       expect(ir.incoming_messages.count).to eq(1)