Question : Exchange 2007 Slow response

We have just installed a new Exchange 2007 box. (migrated from 2003 exchange server)
A lot of the users are complaining that when they frist open Outlook 2007 client, there is a large deplay to open a email.
    Also if they leave outlook open for a while, and do not do anything, there is a delay when they try to open and email (usually 5-15 sec)

I been trying to find a solution for this problem. Is there a way to stop the delays.

Answer : Exchange 2007 Slow response

Never got a answer so I want to close the case