[imp] Problem of using SMTP for sending outgoing though IMP 3.1

[EdwardSPL at ita.org.mo]

Hello,

About our system :
Server A ( host1.123.com ) : imap server  + Sendmail ( redhat 6.2 )  +
DNS
Server B ( host2.123.com ) : Web Server + IMP WebMail System ( redhat
7.2 )

About the Mailer ( smtp ) setting of  horde/imp,
/horde/config/horde.php:

/**
 ** Mailer
 **/

// What method should we use for sending mail? Valid options are
// currently 'sendmail' and 'smtp'.
$conf['mailer']['type'] = 'smtp';

// An array holding any parameters that the Mail object will need to
// function correctly. For sendmail, this is mainly the sendmail_path
// option; SMTP requires at least a server and a port (if nonstandard).
// If you want to use SMTP authentication, set the 'auth' parameter
// to 'true' (without quotes).
// $conf['mailer']['params'] = array();
// $conf['mailer']['params'] = array('sendmail_path' =>
'/usr/lib/sendmail');
// $conf['mailer']['params'] = array('host' => 'smtp.example.com');

My problem :
can't to use edward@123.com post emails to edward@123.com ( for back up
emails ) though IMP, but can use edward@123.com post emails to
edward@123.com though other mail client ( eg : Netscape, Outlook, pine
/etc... )

So, how can I fix this problem ?

Thank you so much !

Edward.