Append Today Date to the Attachement Name using SQL reporting services

I have a report on SQL reporting services, I have scheduled this report to be sent automatically by mail using Subscriptions but the client needs to append today date to the report name attached, currently the attachment is taking the report name as it is. EX: CollectExport.txt but what I need is to have CollectExport_21-07-2010.txt .

Please advise.

Thanks.