right_main.php
define('SM_PATH','../');

/ SquirrelMail required files. /
include_once(SM_PATH . 'include/validate.php');
//include_once(SM_PATH . 'functions/global.php');
require_once(SM_PATH . 'functions/imap.php');
require_once(SM_PATH . 'functions/date.php');
require_once(SM_PATH . 'functions/mime.php');
require_once(SM_PATH . 'functions/mailbox_display.php');
require_once(SM_PATH . 'functions/display_messages.php');
require_once(SM_PATH . 'functions/html.php');
//require_once(SM_PATH . 'functions/plugin.php');
...
Get rid of dynamic paths and _once
include '../include/validate.php';
require '../functions/imap.php';
require '../functions/date.php';
require '../functions/mime.php';
require '../functions/mailbox_display.php';
require '../functions/display_messages.php';
require '../functions/html.php';
Results
** SIEGE 2.66
** Preparing 10 concurrent users for battle.
The server is now under siege..      done.                                                                                                          Transactions:                   10000 hits
Availability:                 100.00 %
Elapsed time:                  57.91 secs
Data transferred:              13.72 MB
Response time:                  0.05 secs
Transaction rate:             172.68 trans/sec
Throughput:                     0.24 MB/sec
Concurrency:                    8.31
Successful transactions:       10000
Failed transactions:               0
Longest transaction:           11.84
Shortest transaction:           0.00