Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 40439)
+++ wp-includes/pluggable.php	(working copy)
@@ -326,13 +326,8 @@
 	 */

 	if ( !isset( $from_email ) ) {
-		// Get the site domain and get rid of www.
-		$sitename = strtolower( $_SERVER['SERVER_NAME'] );
-		if ( substr( $sitename, 0, 4 ) == 'www.' ) {
-			$sitename = substr( $sitename, 4 );
-		}
-
-		$from_email = 'wordpress@' . $sitename;
+		$dom = parse_url( get_home_url( get_current_blog_id() ), PHP_URL_HOST );
+		$from_email = 'wordpress@' . preg_replace("/^.*?([^\.]+)\.([^\.]+)$/", "$1.$2", $dom);
 	}

 	/**