Please remove the ending php tag at the end of wp-mail-bank.php. I have Yoast sitemap plugin installed and the ending space in the PHP file generates a space at the top of my XML file, rendering it invalid.
register_uninstall_hook(__FILE__, "plugin_uninstall_hook_for_mail_bank");
add_action("in_plugin_update_message-".MAIL_FILE,"mail_bank_plugin_update_message" );
?> // Remove this line
// Space is here