SquirrelMail runs slow with bigger inboxes

If you experience problems with squirrelmail running slow on inboxes with lots 
of e-mails, then the problem is with who's handling the sorting. 
Normally, the imap server is capable of doing this sorting server side, which is
alot faster than doing it in php (client side, which in this case would be
squirrelmail). If the imap server doesn't support sorting, consider switching to
another imap server.
To make squirrelmail use the advantages of server side sorting, locate the
following lines in /path/to/squirrelmail/config/config.php and make sure they're
both set to "true":

    $allow_thread_sort        = true;
    $allow_server_sort        = true;

That should set things straight!