FIX: deleting staged user of rejected email shouldn't delete incoming email

lib/email/receiver.rb

@@ -756,7 +756,13 @@ module Email
 
     def delete_staged_users
       @staged_users.each do |user|
-        UserDestroyer.new(Discourse.system_user).destroy(user, quiet: true) if user.posts.count == 0
+        if @incoming_email.user.id == user.id
+          @incoming_email.update_columns(user_id: nil)
+        end
+
+        if user.posts.count == 0
+          UserDestroyer.new(Discourse.system_user).destroy(user, quiet: true)
+        end
       end
     end
   end

spec/components/email/receiver_spec.rb

@@ -760,6 +760,11 @@ describe Email::Receiver do
       end
     end
 
+    it "does not remove the incoming email record when staged users are deleted" do
+      expect { process(:bad_destinations) }.to change { IncomingEmail.count }
+        .and raise_error(Email::Receiver::BadDestinationAddress)
+      expect(IncomingEmail.last.message_id).to eq("9@foo.bar.mail")
+    end
   end
 
 end