[imp] Imp+sorting=terrible slow down

[Joe7]

Hello Experts,
I just realized that my problem with mailboxes -which has more then 
10.000mails in inbox-,
IS sorting. (if I disable this in courier imapd config,
everything goes at lightning speed, login takes <1sec (instead of 
1MINUTE or failure), and to go to
the next page in inbox is just about 1sec instead of 30..
So my question is how to make sorting faster.
I guess the way to do it on the serverside, not in "processing time"..
But how? Does IMP support ir someway? :O

Thanks any idea in advance,

Joe RN.