E-mails not deleted after a download

I just got a new computer and when I download e-mail on to my computer, it stays on the web site and when I get e-mail later that day, the previous e-mails I downloaded are still there and they are now duplicated on my hard drive. I get hundreds of e-mails per day and besides being a hastle, I will reach my quota pretty quickly. Thank you. X@riseup.net Since this didn't happen with my previous computer, I assume some setting got changed. I hope this is one of those easy-when-you-know-how things. (PII redacted by moderator)