Read messages per page not all the message inbox

[mymail]

Hello,

I've an inbox with 3000 messages, with imap debug enabled, and cache enabled.
I've configured 20 messages per page.
But when I read the imap debug I can see that fetch all the 3000 messages.
How can I improve this performance?

Best regards,

myMail

[alec]

Change sorting order (best performance is with None).