[imp]SMTP Mailer

[Jorge Izquierdo]

Hello again. I´m trying to send mail without sendmail running on the machine
where my IMP is installed. I´ve configured the values for this objective:

$conf['mailer']['type'] = 'smtp';
$conf['mailer']['params'] = array('server' => 'smtphost.mydomain.es');

in horde.php file and added th line of smtphost to my IMAP server on
servers.php:

    'smtphost' => 'smtphost.mydomain.es',

but I get an error when I try to send a message (with next info in horde.log):

mar 04 14:23:30 HORDE [error] [imp] unable to connect to smtp server
localhost:25 [on line 787 of "/www/horde/imp/compose.php"]

Is necessary to have a sendmail running on the machine where IMP is installed?
Or should it be possible the php code to connect directly to the smtp server
specified on my configuration params.

Thanks for your attention.

Jorge