warning: mail() has been disabled for security reasons

warning: mail() has been disabled for security reasons in /home/.../includes/common.inc on line 1991.

in file common.inc online 1935 - 1993

function drupal_mail($mailkey, $to, $subject, $body, $from = NULL, $headers = array()) {
  $defaults = array(
    'MIME-Version' => '1.0',
    'Content-Type' => 'text/plain; charset=UTF-8; format=flowed',
    'Content-Transfer-Encoding' => '8Bit',
    'X-Mailer' => 'Drupal'
  );
  // To prevent e-mail from looking like spam, the addresses in the Sender and
  // Return-Path headers should have a domain authorized to use the originating
  // SMTP server.  Errors-To is redundant, but shouldn't hurt.
  $default_from = variable_get('site_mail', ini_get('sendmail_from'));
  if ($default_from) {
    $defaults['From'] = $defaults['Reply-To'] = $defaults['Sender'] = $defaults['Return-Path'] = $defaults['Errors-To'] = $default_from;
  }
  if ($from) {
    $defaults['From'] = $defaults['Reply-To'] = $from;
  }
  $headers = array_merge($defaults, $headers);
  // Custom hook traversal to allow pass by reference
  foreach (module_implements('mail_alter') AS $module) {
    $function = $module .'_mail_alter';
    $function($mailkey, $to, $subject, $body, $from, $headers);
  }
  // Allow for custom mail backend
  if (variable_get('smtp_library', '') && file_exists(variable_get('smtp_library', ''))) {
    include_once './' . variable_get('smtp_library', '');
    return drupal_mail_wrapper($mailkey, $to, $subject, $body, $from, $headers);
  }
  else {
    // Note: if you are having problems with sending mail, or mails look wrong
    // when they are received you may have to modify the str_replace to suit
    // your systems.
    //  - \r\n will work under dos and windows.
    //  - \n will work for linux, unix and BSDs.
    //  - \r will work for macs.
    //
    // According to RFC 2646, it's quite rude to not wrap your e-mails:
    //
    // "The Text/Plain media type is the lowest common denominator of
    // Internet e-mail, with lines of no more than 997 characters (by
    // convention usually no more than 80), and where the CRLF sequence
    // represents a line break [MIME-IMT]."
    //
    // CRLF === \r\n
    //
    // http://www.rfc-editor.org/rfc/rfc2646.txt

    $mimeheaders = array();
    foreach ($headers as $name => $value) {
      $mimeheaders[] = $name .': '. mime_header_encode($value);
    }
    return mail(
      $to,
      mime_header_encode($subject),
      str_replace("\r", '', $body),
      join("\n", $mimeheaders)
    );
  }
}

My host linux.
in PHP Configuration

  Sub Section  	Directive  	Info  	Value
Language Options 	asp_tags 	Allow ASP-style <% %> tags. 	Off
File Uploads 	file_uploads 	Whether to allow HTTP file uploads. 	On
Paths and Directories 	include_path 	Windows: "\path1;\path2" 	.:/usr/lib/php:/usr/local/lib/php
Resource Limits 	max_execution_time 		30
Resource Limits 	max_input_time 		60
Resource Limits 	memory_limit 		20M
Data Handling 	register_globals 	You should do your best to write your scripts so that they do not require register_globals to be on; Using form variables as globals can easily lead to possible security problems, if the code is not very well thought of. 	On
Language Options 	safe_mode 		Off
main 	session.save_path 	Argument passed to save_handler. In the case of files, this is the path where data files are stored. Note: Windows users have to change this variable in order to use PHP's session functions. As of PHP 4.0.1, you can define the path as: where N is an integer. Instead of storing all the session files in /path, what this will do is use subdirectories N-levels deep, and store the session data in those directories. This is useful if you or your OS have problems with lots of files in one directory, and is a more efficient layout for servers that handle lots of sessions. NOTE 1: PHP will not create this directory structure automatically. You can use the script in the ext/session dir for that purpose. NOTE 2: See the section on garbage collection below if you choose to use subdirectories for session storage 	/tmp
File Uploads 	upload_max_filesize 	Maximum allowed size for uploaded files. 	8M
main 	zend_optimizer.version 		3.3.0

Help me!
Thanks!