Index: wp-admin/network/settings.php
===================================================================
--- wp-admin/network/settings.php	(revision 18666)
+++ wp-admin/network/settings.php	(working copy)
@@ -44,6 +44,8 @@
 
 	if ( is_email( $_POST['admin_email'] ) )
 		update_site_option( 'admin_email', $_POST['admin_email'] );
+	else
+		wp_die( __( 'Invalid email address.' ) );
 
 	$illegal_names = split( ' ', $_POST['illegal_names'] );
 	foreach ( (array) $illegal_names as $name ) {