FIX: Try fixing unparsable email addresses

The mail gem returns `UnstructuredField` when it fails to parse email addresses, but the `Receiver` always expects an `AddressList`.

lib/email/receiver.rb

@@ -64,6 +64,7 @@ module Email
       DistributedMutex.synchronize(@message_id) do
         begin
           return if IncomingEmail.exists?(message_id: @message_id)
+          ensure_valid_address_lists
           @from_email, @from_display_name = parse_from_field(@mail)
           @incoming_email = create_incoming_email
           process_internal
@@ -77,6 +78,16 @@ module Email
       end
     end
 
+    def ensure_valid_address_lists
+      [:to, :cc, :bcc].each do |field|
+        addresses = @mail[field]
+
+        if addresses&.errors.present?
+          @mail[field] = addresses.to_s.scan(/\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b/i)
+        end
+      end
+    end
+
     def is_blacklisted?
       return false if SiteSetting.ignore_by_title.blank?
       Regexp.new(SiteSetting.ignore_by_title, Regexp::IGNORECASE) =~ @mail.subject

spec/components/email/receiver_spec.rb

@@ -886,4 +886,12 @@ describe Email::Receiver do
       end
     end
   end
+
+  it "tries to fix unparsable email addresses in To, CC and BBC headers" do
+    expect { process(:unparsable_email_addresses) }.to raise_error(Email::Receiver::BadDestinationAddress)
+
+    email = IncomingEmail.last
+    expect(email.to_addresses).to eq("foo@bar.com")
+    expect(email.cc_addresses).to eq("bob@example.com;carol@example.com")
+  end
 end

spec/fixtures/emails/unparsable_email_addresses.eml

@@ -0,0 +1,7 @@
+Date: 27 Mar 2018 11:51:04 +0200
+From: alice@example.com
+To: foo@bar.com.
+CC: bob@example.com., carol@example.com.
+Subject: Email addresses ending with dot
+
+Lorem ipsum