Since I sort my emails with the latest at the top, these sink to the bottom. I know they are there when my email client tells me that I have new emails, but no unread emails are at the top of the inbox window. I scroll to the bottom of the window and there they sit, as spammy as they can be.
The only rationale I can see for this is that the spammers can tell their clients that their spams have been sent and received.
I note that, when I visit my ISP’s webmail interface, the emails are displayed in the order received, so this sort of spam does not sink to the bottom there. And I do visit my ISP’s webmail interface from time to time, so I can mark spam as spam and help my ISP improve its spam filters, which effort has seems to yield results.
I started doing this when the amount of spam emails I received spiked late last year. Spams disappeared for while, but they have lately started back up, because it’s a never-ending story.
In a related note, there is a long thread at LQ inquiring as to why persons use mail clients rather than webmail.