Autoban dmail spambots (#3408).

If a user sends spam to more than 10 users within a 24 hour window,
automatically ban them for 3 days.

test/unit/dmail_test.rb

@@ -3,6 +3,7 @@ require 'test_helper'
 class DmailTest < ActiveSupport::TestCase
   context "A dmail" do
     setup do
+      User.any_instance.stubs(:validate_sock_puppets).returns(true)
       @user = FactoryGirl.create(:user)
       CurrentUser.user = @user
       CurrentUser.ip_addr = "1.2.3.4"
@@ -27,6 +28,20 @@ class DmailTest < ActiveSupport::TestCase
           assert(@recipient.dmails.last.is_spam?)
         end
       end
+
+      should "autoban spammers after sending spam to N distinct users" do
+        Dmail.any_instance.expects(:spam?).returns(true)
+
+        users = FactoryGirl.create_list(:user, Dmail::AUTOBAN_THRESHOLD)
+        users.each do |user|
+          Dmail.create_split(from: @user, to: user, title: "spam", body: "wonderful spam")
+        end
+
+        assert_equal(true, Dmail.is_spammer?(@user))
+        assert_equal(true, @user.reload.is_banned)
+        assert_equal(1, @user.bans.count)
+        assert_match(/Spambot./, @user.bans.last.reason)
+      end
     end
 
     context "filter" do