diff --git a/guides/source/4_0_release_notes.md b/guides/source/4_0_release_notes.md
index 002e1da5af..95b57ec899 100644
--- a/guides/source/4_0_release_notes.md
+++ b/guides/source/4_0_release_notes.md
@@ -7,7 +7,6 @@ Highlights in Rails 4.0:
 * Strong Parameters
 * Turbolinks
 * Russian Doll Caching
-* Asynchronous Mailers
 
 These release notes cover only the major changes. To know about various bug fixes and changes, please refer to the change logs or check out the [list of commits](https://github.com/rails/rails/commits/master) in the main Rails repository on GitHub.