Index: src/includes/core/filters.php
===================================================================
--- src/includes/core/filters.php
+++ src/includes/core/filters.php
@@ -262,6 +262,16 @@
 add_filter( 'bbp_make_clickable', 'bbp_make_emails_clickable',    6 ); // jjj@bbpress.org
 add_filter( 'bbp_make_clickable', 'bbp_make_mentions_clickable',  8 ); // @jjj
 
+/*
+ * Emails - If WordPress is 4.3+, return null for the 'To' email address.
+ *
+ * This will allow PHPMailer to set the 'To' email header to
+ * 'undisclosed-recipients;' for those using PHP's mail()
+ */
+if ( function_exists( 'wptexturize_primes' ) ) {
+	add_filter( 'bbp_subscription_to_email', '__return_null' );
+}
+
 /** Deprecated ****************************************************************/
 
 /**