diff --git src/wp-includes/user.php src/wp-includes/user.php
index 3d2bf939d4..2b6e28f64a 100644
--- src/wp-includes/user.php
+++ src/wp-includes/user.php
@@ -1436,7 +1436,14 @@ function email_exists( $email ) {
 	if ( $user ) {
 		return $user->ID;
 	}
-	return false;
+
+	/**
+	 * Filters whether the given email exists or not.
+	 *
+	 * @param int|false $user_id The user's ID on success, and false on failure.
+	 * @param string    $email   Email to check.
+	 */
+	return apply_filters( 'email_exists', $user_id, $email );
 }
 
 /**