Thax for the hint's 
I'v already got some results:
# ================= DO NOT MODIFY THIS FILE =================
#
# Manual changes will be lost when this file is regenerated.
#
# Please read the developer's guide, which is available
# at https://dev.nethesis.it/projects/nethserver/wiki/NethServer
# original work from http://www.contribs.org/development/
#
# Copyright (C) 2013 Nethesis S.r.l.
# http://www.nethesis.it - support@nethesis.it
#
{
/* 10 Database configuration (mysql) */
// Here comes mysql
/* 20 Mail */
SOGoDraftsFolderName = Drafts;
SOGoSentFolderName = Sent;
SOGoTrashFolderName = Trash;
SOGoJunkFolderName = Junk;
SOGoIMAPServer = 'localhost';
SOGoSieveServer = 'sieve://127.0.0.1:4190';
SOGoSMTPServer = '127.0.0.1:587';
SOGoMailDomain = havak.lan;
SOGoMailingMechanism = 'smtp';
NGImap4ConnectionStringSeparator = "/";