Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 17444)
+++ wp-includes/pluggable.php	(working copy)
@@ -420,9 +420,6 @@
 		}
 	}
 
-	// Set to use PHP's mail()
-	$phpmailer->IsMail();
-
 	// Set Content-Type and charset
 	// If we don't have a content-type from the input headers
 	if ( !isset( $content_type ) )