Problem with Yahoo spam in Mail
I'm currently a Mail Plus customer (not sure if I will continue). I'm using Mac OSX ver 10.7.4, Mail ver 5.2. In Mac OSX Mail desktop mail client, I was using IMAP to access my email account. Yesterday, spam emails (that are actually marked as spam by Yahoo, not something that slipped by the filters) started showing up as unread emails in the Yahoo Bulk Folder in my desktop Mail. I tried deleting the bulk folder, but got an error message that isn't allowed. The only way I can see to get rid of the spam emails without looking at them and opening them is to open the yahoo webpage and delete them from there. Sort of negates the value of paying for Mail Plus. I've currently switched to POP, but prefer IMAP, so I don't have to delete the same messages on all my devices.
How do I prevent Yahoo spam emails in the bulk folder from showing up in my desktop Mail client?