An enhancement to e-mail user interfaces and message formats includes a dynamic preview window to view and retrieve attachments and summaries of e-mail messages directly in the e-mail list view or inbox view without opening an e-mail message. The efficient viewing mechanism further allows previews without cluttering the listing of the e-mails in the inbox by allowing the client to detect special preview instructions within an e-mail and run executables within the preview window. The enhancement is applicable to standalone e-mail clients (POP or IMAP based) and to web-based e-mail systems.