Put these config values in config.php:

#GO will connect to this installation to add a mailbox. It is the full url to the Group-Office installation with the postfixadmin module installed.
$config['serverclient_server_url']='http://localhost/groupoffice/';
$config['serverclient_username']='administrator';
$config['serverclient_password']='somepass';

#comma separated list of mailbox domains
$config['serverclient_domains']='intermeshdev.nl';

#The email account properties that will be added for the user
$config['serverclient_mbroot'] = '';
$config['serverclient_use_ssl'] = '0';
$config['serverclient_novalidate_cert'] = '0';
$config['serverclient_type']='imap';
$config['serverclient_host']='localhost';
$config['serverclient_port']=143;
$config['serverclient_smtp_host']='localhost';
$config['serverclient_smtp_port']=25;
$config['serverclient_smtp_encryption']='';
$config['serverclient_smtp_username']='';
$config['serverclient_smtp_password']='';