diff --git a/app/mailers/request_mailer.rb b/app/mailers/request_mailer.rb
index fa42e853f9d..034694c3451 100644
--- a/app/mailers/request_mailer.rb
+++ b/app/mailers/request_mailer.rb
@@ -209,6 +209,21 @@ def comment_on_alert_plural(info_request, count, earliest_unalerted_comment)
     )
   end
 
+
+  def guess_email_request_address(email)
+    # Match the email address in the message without matching the hash
+    guess_addresses = MailHandler.get_all_addresses(email)
+    guessed_info_requests =
+      InfoRequest.guess_by_incoming_email(guess_addresses)
+
+    # Match the email subject in the message
+    guess_by_subject =
+      InfoRequest.guess_by_incoming_subject(email.subject)
+    (guessed_info_requests + guess_by_subject).
+      select(&:info_request).uniq(&:info_request).
+      map { |ir_guess| ir_guess.info_request }
+  end
+
   # Class function, called by script/mailin with all incoming responses.
   # [ This is a copy (Monkeypatch!) of function from action_mailer/base.rb,
   # but which additionally passes the raw_email to the member function, as we
@@ -232,38 +247,65 @@ def self.receive(raw_email, source = :mailin)
   # Find which info requests the email is for
   def requests_matching_email(email)
     addresses = MailHandler.get_all_addresses(email)
-    InfoRequest.matching_incoming_email(addresses)
+    addresses.concat MailHandler.get_emails_within_received_headers(email)
+    InfoRequest.matching_incoming_email(addresses.uniq)
+  end
+
+  def send_to_holding_pen(email, raw_email, opts)
+    opts[:rejected_reason] =
+    _("Could not identify the request from the email address")
+    request = InfoRequest.holding_pen_request
+    request.receive(email, raw_email, opts)
   end
 
   # Member function, called on the new class made in self.receive above
   def receive(email, raw_email, source = :mailin)
     opts = { source: source }
+    # Only check mail that doesn't have spam in the header
+    unless SpamAddress.spam?(MailHandler.get_all_addresses(email))
+      used_guesses = false
+      # Find exact matches for info requests
+      reply_info_requests = requests_matching_email(email)
+
+      # Find any guesses for info requests
+      guessed_info_requests = guess_email_request_address(email)
+      # If there are any guesses which aren't already in the reply_info_requests
+      # then add them, and set the 'used_guesses' flag to true for event logging
+      guessed_info_requests.each do |guess|
+        unless reply_info_requests.include?(guess)
+          reply_info_requests.append(guess)
+          used_guesses = true
+        end
+      end
 
-    # Find which info requests the email is for
-    reply_info_requests = requests_matching_email(email)
-
-    # Nothing found OR multiple different info requests, so save in holding pen
-    if reply_info_requests.empty? || reply_info_requests.count > 1
-      opts[:rejected_reason] =
-        _("Could not identify the request from the email address")
-      request = InfoRequest.holding_pen_request
+      # If there is only one info request matching mail, it gets attached to the
+      # request to be archived with it
+      if reply_info_requests.count == 1 and guessed_info_requests.count < 2
+        reply_info_request = reply_info_requests.first
 
-      unless SpamAddress.spam?(MailHandler.get_all_addresses(email))
-        request.receive(email, raw_email, opts)
-      end
-      return
-    end
+        # If environment variable STOP_DUPLICATES is set, don't send message
+        # with same id again
+        if ENV['STOP_DUPLICATES']
+          if reply_info_request.already_received?(email, raw_email)
+            raise "message #{ email.message_id } already received by request"
+          end
+        end
 
-    # Send the message to each request, to be archived with it
-    reply_info_requests.each do |reply_info_request|
-      # If environment variable STOP_DUPLICATES is set, don't send message with same id again
-      if ENV['STOP_DUPLICATES']
-        if reply_info_request.already_received?(email, raw_email)
-          raise "message #{ email.message_id } already received by request"
+        if used_guesses
+          reply_info_request.log_event(
+            'redeliver_incoming',
+            editor: 'automatic',
+            destination_request: reply_info_request,
+          )
         end
-      end
 
-      reply_info_request.receive(email, raw_email, opts)
+        reply_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
+        send_to_holding_pen(email, raw_email, opts)
+      end
     end
   end
 
diff --git a/spec/integration/admin_spec.rb b/spec/integration/admin_spec.rb
index e298236a4a3..edfc4c0a962 100644
--- a/spec/integration/admin_spec.rb
+++ b/spec/integration/admin_spec.rb
@@ -127,26 +127,6 @@
         expect(page).to have_content "Only the authority can reply to this request"
       end
     end
-
-    it "guesses a misdirected request" do
-      info_request = FactoryBot.create(:info_request,
-                                       allow_new_responses_from: 'authority_only',
-                                       handle_rejected_responses: 'holding_pen')
-      mail_to = "request-#{info_request.id}-asdfg@example.com"
-      receive_incoming_mail('incoming-request-plain.email', email_to: mail_to)
-      interesting_email = last_holding_pen_mail
-
-      # now we add another message to the queue, which we're not interested in
-      receive_incoming_mail('incoming-request-plain.email',
-                            email_to: info_request.incoming_email,
-                            email_from: "")
-      expect(holding_pen_messages.length).to eq(2)
-      using_session(@admin) do
-        visit admin_raw_email_path interesting_email
-        expect(page).to have_content "Could not identify the request"
-        expect(page).to have_content info_request.title
-      end
-    end
   end
 
   describe 'generating an upload url' do
diff --git a/spec/mailers/request_mailer_spec.rb b/spec/mailers/request_mailer_spec.rb
index 07a93433d3c..5354a0ce6cb 100644
--- a/spec/mailers/request_mailer_spec.rb
+++ b/spec/mailers/request_mailer_spec.rb
@@ -20,7 +20,26 @@
       deliveries = ActionMailer::Base.deliveries
       expect(deliveries.size).to eq(1)
       mail = deliveries[0]
-      expect(mail.to).to eq([ 'bob@localhost' ]) # to the user who sent fancy_dog_request
+      # to the user who sent fancy_dog_request
+      expect(mail.to).to eq(['bob@localhost'])
+      deliveries.clear
+    end
+
+    it "should append it to the appropriate request if there is only one guess of information request" do
+      ir = info_requests(:fancy_dog_request)
+      expect(ir.incoming_messages.count).to eq(1) # in the fixture
+      receive_incoming_mail(
+        'incoming-request-plain.email',
+        email_to: "request-#{ir.id}-#{ir.idhash}a@localhost"
+      )
+      expect(ir.incoming_messages.count).to eq(2) # one more arrives
+      expect(ir.info_request_events[-1].incoming_message_id).not_to be_nil
+
+      deliveries = ActionMailer::Base.deliveries
+      expect(deliveries.size).to eq(1)
+      mail = deliveries[0]
+      # to the user who sent fancy_dog_request
+      expect(mail.to).to eq(['bob@localhost'])
       deliveries.clear
     end
 
@@ -48,7 +67,6 @@
       expect(InfoRequest.holding_pen_request.incoming_messages.count).to eq(1)
     end
 
-
     it "attaches messages with an info request address in the Received headers to the appropriate request" do
       ir = info_requests(:fancy_dog_request)
       expect(ir.incoming_messages.count).to eq(1) # in the fixture
@@ -69,7 +87,8 @@
       deliveries = ActionMailer::Base.deliveries
       expect(deliveries.size).to eq(1)
       mail = deliveries[0]
-      expect(mail.to).to eq([ 'bob@localhost' ]) # to the user who sent fancy_dog_request
+      # to the user who sent fancy_dog_request
+      expect(mail.to).to eq(['bob@localhost'])
       deliveries.clear
     end