ExceptionHook.php

<?php

class ExceptionHook 
{
  public function SetExceptionHandler()
  {
    set_exception_handler(array($this, 'HandleExceptions'));
  }
   
  public function HandleExceptions($exception)
  {
	
  	$msg ='Exception of type \''.get_class($exception).'\' occurred with Message: '.$exception->getMessage().' in File '.$exception->getFile().' at Line '.$exception->getLine();
		
        $msg .="\r\n Backtrace \r\n";
	$msg .=$exception->getTraceAsString();
	
        log_message('error', $msg, TRUE);
	
        		
	mail('[email protected]', 'An Exception Occurred', $msg, 'From: [email protected]');	

	
}

MY_Exceptions.php

<?php

class MY_Exceptions extends CI_Exceptions {

    public function __construct()
    {
	
        parent::CI_Exceptions();
    }

    public function show_php_error($severity, $message, $filepath, $line)
    {	
	$severity = ( ! isset($this->levels[$severity])) ? $severity : $this->levels[$severity];
	$filepath = str_replace("\\", "/", $filepath);
	
	// For safety reasons we do not show the full file path
	if (FALSE !== strpos($filepath, '/'))
	{
            $x = explode('/', $filepath);
	    $filepath = $x[count($x)-2].'/'.end($x);
	}
		
	if (ob_get_level() > $this->ob_level + 1)
	{
	    ob_end_flush();	
	}
	ob_start();
	include(APPPATH.'errors/error_php'.EXT);
	$buffer = ob_get_contents();
	ob_end_clean();
		
	$msg = 'Severity: '.$severity.'  --> '.$message. ' '.$filepath.' '.$line;

        log_message('error', $msg , TRUE);

	mail('[email protected]', 'An Error Occurred', $msg, 'From: [email protected]');	
	
    }

}

You need to set
$config['subclass_prefix'] = 'MY_'; in config.php file

Did you ever find the solution to this @lomse
I have $config['subclass_prefix'] = 'MY_';

but still getting Class 'CI_Exceptions' not found