Squirrelmail IMAP mbox

[Brenden Eng <brendeneng@gmail.com>]

Hello, Currently my email server (600Mhz p3) is having some trouble
with mail boxes with more than 1000mails (each one is < 5kb).  Regular
IMAP access through a client (ex mutt, endura, outlook) is fast. 
telnetting to the server and doing SELECT INBOX is also relatively
fast, taking about .5 seconds.

However, logging into the account on squirrelmail takes about 30
seconds for a page to load which is not very productive.  The user has
about 30 mailboxes into which he (manually) distributes the mail from
the inbox.

Perhaps the large number of folders could be bogging down the server?
I notice uw-imapd cpu usage near 100% when the user is logging in.

I know the server is a bit on the slow side but are there any tweaks? 
Perhaps switching to Maildir and using courier-imap?

Thanks.
Brenden Eng