0. make a backup of your RC !!!

1. edit file index.php in main RC webdir and after
"include_once('program/steps/settings/func.inc');"
add
if ($_action=='autoreply' || $_action=='save-autoreply')
include('program/steps/settings/autoreply.inc');

result like below

(...)
// include task specific files
if ($_task=='settings')
{
include_once('program/steps/settings/func.inc');
if ($_action=='autoreply' || $_action=='save-autoreply')
include('program/steps/settings/autoreply.inc');
(...)

2. edit file program/steps/settings/func.inc, look for
"// register UI objects
$OUTPUT->add_handlers(array(
'userprefs' => 'rcmail_user_prefs_form',
'itentitieslist' => 'rcmail_identities_list',"
next add line
'autoreply' => 'rcmail_autoreply_form',

result like below

(...)
// register UI objects
$OUTPUT->add_handlers(array(
'userprefs' => 'rcmail_user_prefs_form',
'itentitieslist' => 'rcmail_identities_list',
'autoreply' => 'rcmail_autoreply_form'
));


3. edit file program/js/app.js, search for "case 'settings':"
change line
this.enable_command('preferences', 'identities', 'save', 'folders', true);
to
this.enable_command('preferences', 'identities', 'save', 'folders', 'autoreply', true);
and just below add the following:
if ( this.env.action=='autoreply' || this.env.action=='save-autoreply' ) {
var input_active = rcube_find_object('_active_autoreply');
var input_tekst = rcube_find_object('_tekst_autoreply');
this.enable_command('save-autoreply', true);
}

result like below

(...)
case 'settings':
this.enable_command('preferences', 'identities', 'save', 'folders', 'autoreply', true);
if ( this.env.action=='autoreply' || this.env.action=='save-autoreply' ) {
var input_active = rcube_find_object('_active_autoreply');
var input_tekst = rcube_find_object('_tekst_autoreply');
this.enable_command('save-autoreply', true);
}
(...)

in the same file program/js/app.js look for
"this.delete_folder(props);
break;"
and just below add next lines:
case 'autoreply':
this.goto_url('autoreply');
break;

case 'save-autoreply':
var input_active = rcube_find_object('_active_autoreply');
var input_tekst = rcube_find_object('_tekst_autoreply');
this.gui_objects.editform.submit();
break;

result like below

(...)
case 'delete-folder':
if (confirm(this.get_label('deletefolderconfirm')))
this.delete_folder(props);
break;

case 'autoreply':
this.goto_url('autoreply');
break;

case 'save-autoreply':
var input_active = rcube_find_object('_active_autoreply');
var input_tekst = rcube_find_object('_tekst_autoreply');
this.gui_objects.editform.submit();
break;
(...)

4. enter directory program/steps/settings/ and download file
http://daniel.blogs.jebiemnieto.org/files/2007/07/autoreplyinc.txt, rename it to
autoreply.inc and make sure that owner and group is the same as the rest of files in this dir

5. edit autoreply.inc and modify function rcmail_save_autoreply and rcmail_autoreply_form($attrib)
my mta user table have uniq id ("id") and every user afer succesfull login into RC "gets" session
variable ("$_SESSION['adnet_id']") in which i store users id. this is done in program/include/main.inc
file in function rcmail_login($user, $pass, $host=NULL)
<after
// user already registered -> overwrite username
if ($sql_arr = $DB->fetch_assoc($sql_result))
{
$user_id = $sql_arr['user_id'];
$user = $sql_arr['username'];
}
i added
@ $DB_1 = new mysqli('localhost', 'adnetmail', 'VerySecurePassword123456', 'adnet_mail');
$RESULT_1 = $DB_1->query('SELECT id FROM v_daemon WHERE email = \'' . $user . '\'');
$ROWS_1 = $RESULT_1->num_rows;
if ( $ROWS_1 == 1 ) {
$ROW_2 = $RESULT_1->fetch_assoc();
$adnet_id = $ROW_2['id'];
$_SESSION['adnet_id'] = $adnet_id;
}
$DB_1->close();

how you can see in this file you can customize getting user id from mta database (if you have to) or you can
skip this simply just modifing only rcmail_save_autoreply and rcmail_autoreply_form functions in autoreply.inc,
to update fileds in your table.

6. download template http://daniel.blogs.jebiemnieto.org/files/2007/07/autoreplyhtml.txt and
save as autoreply.html into skins/default/templates/ and also make sure httpd can access to the file.

7. edit program/localization/en_US/labels.inc adding lines

$labels['autoreply'] = 'Autoreply';
$labels['titleautoreply'] = 'Autoreply settings';
$labels['activeautoreply'] = 'Autoresponder active';
$labels['textautoreply'] = 'Autoresponder text';

8. edit program/localization/en_US/messages.inc adding lines

$messages['autoreplymodified'] = 'Autoresponder settings saved.';
$messages['noautoreply'] = 'Autoreponder active but no text provided.';

You can also expand this messages and labels to your language, just edit files
program/localization/${yours_lang}/{labels.inc,messages.inc} but remember to encode it with utf-8

9. edit file skins/default/includes/settingstabs.html, make sure its like this

<div id="tabsbar">
<span id="settingstabdefault" class="tablink"><roundcube:button command="preferences" type="link" label="preferences" 
title="editpreferences" /></span>
<span id="settingstabfolders" class="tablink"><roundcube:button command="folders" type="link" label="folders" title="managefolders" 
class="tablink" /></span>
<span id="settingstabidentities" class="tablink"><roundcube:button command="identities" type="link" label="identities" 
title="manageidentities" class="tablink" /></span>
<span id="settingstabautoreply" class="tablink"><roundcube:button command="autoreply" type="link" label="autoreply" title="titleautoreply" 
class="tablink" /></span>
</div>



10. I belive thats all :)