diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index 8e358b4293..edfd5e2cd1 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add `rails test:mailboxes`.
+
+    *George Claghorn*
+
 *   Introduce guard against DNS rebinding attacks
 
     The `ActionDispatch::HostAuthorization` is a new middleware that prevent
diff --git a/railties/lib/rails/test_unit/testing.rake b/railties/lib/rails/test_unit/testing.rake
index 32ac27a135..ecc458b21e 100644
--- a/railties/lib/rails/test_unit/testing.rake
+++ b/railties/lib/rails/test_unit/testing.rake
@@ -28,7 +28,7 @@ namespace :test do
   desc "Run tests quickly, but also reset db"
   task db: %w[db:test:prepare test]
 
-  ["models", "helpers", "controllers", "mailers", "integration", "jobs"].each do |name|
+  ["models", "helpers", "controllers", "mailers", "integration", "jobs", "mailboxes"].each do |name|
     task name => "test:prepare" do
       $: << "test"
       Rails::TestUnit::Runner.rake_run(["test/#{name}"])
diff --git a/railties/test/application/test_runner_test.rb b/railties/test/application/test_runner_test.rb
index 55ce72181f..6765eef9d0 100644
--- a/railties/test/application/test_runner_test.rb
+++ b/railties/test/application/test_runner_test.rb
@@ -131,6 +131,18 @@ module ApplicationTests
       end
     end
 
+    def test_run_mailboxes
+      create_test_file :mailboxes, "foo_mailbox"
+      create_test_file :mailboxes, "bar_mailbox"
+      create_test_file :models, "foo"
+
+      rails("test:mailboxes").tap do |output|
+        assert_match "FooMailboxTest", output
+        assert_match "BarMailboxTest", output
+        assert_match "2 runs, 2 assertions, 0 failures", output
+      end
+    end
+
     def test_run_functionals
       create_test_file :mailers, "foo_mailer"
       create_test_file :controllers, "bar_controller"
@@ -155,11 +167,11 @@ module ApplicationTests
     end
 
     def test_run_all_suites
-      suites = [:models, :helpers, :unit, :controllers, :mailers, :functional, :integration, :jobs]
+      suites = [:models, :helpers, :unit, :controllers, :mailers, :functional, :integration, :jobs, :mailboxes]
       suites.each { |suite| create_test_file suite, "foo_#{suite}" }
       run_test_command("") .tap do |output|
         suites.each { |suite| assert_match "Foo#{suite.to_s.camelize}Test", output }
-        assert_match "8 runs, 8 assertions, 0 failures", output
+        assert_match "9 runs, 9 assertions, 0 failures", output
       end
     end