Mail Settings

I have been away for several months due to illness. When I logged back in I had more than 4,000 email messages! The "Select All" feature only selects what is on the screen. You can imagine how long it took for me to delete everything 25 messages at a time.
Is there a setting that will let me turn OFF certain emails? Is there a way to select ALL of the messages for deletion instead of a page at a time? Thanks for your help. 

there should be but from my understanding i dont think so you just have to delete all them 25 at a time 

Get a desktop client that allows you to download headers only (Foxmail is one), and then delete on server.

I would still take a while to download all the headers, but at least its automatic, and you can do something else in the meantime