you mail want to download a small program such as Mailmoa (www.moazon.com) that will read the headers of the mail records rather than the whole message. Then you can delete it easily.

Your other choice is to use a web mailer (like hotmail and yahoo) that give you the ability to "check external mail" from your ISP. Then you can setup and download the mail into your yahoo mailbox and delete it from there.

if you need help getting the mailmoa program or getting it going let me know.