mail question

When I was using Tiger on my emac (RIP), I read in one of the forums that by moving the bar (that separates the mail messages from the previews) down to the bottom of the window, you could delete the email without it ever having been shown that you looked at it. I am now using a new iMac, Lion os 10.7.3, and see that the blue dot which indicates a message is new, disappears when you have the bar moved up to preview the message. So, this is not marked as received on sender's side, if you delete it after previewing, or has that been changed?

Thanks!