I wanted to add the Memcache feature that horde offers, but at the apache logs appeared that Horde_Memcache class not found. This is already a known situation. The onlything you have to do is to install with pear the class of horde project needed.
In order to do this, just type at command promt:
pear install horde/Horde_Memcache
If you have enabled the datatree backend at horde main settings then you have to install the Horde_Datatree package from pear.
pear install horde/Horde_Datatree
After this procedure I was able to configure the backend of the datatree.
If you have enabled the smtp server at horde mailer settings then you have to install the Net_SMTP package from pear.
You can check your conf.php file under config folder
One way to do this is to cat this file and grep mailer
cat conf.php | grep mailer
$conf['mailer']['params']['host'] = 'mail.example.com';
$conf['mailer']['params']['port'] = 25;
$conf['mailer']['params']['auth'] = true;
$conf['mailer']['type'] = 'smtp';
I was not able to send mail from the webmail, and I check the logs from apache. I saw these logs:
tail -f apache_error.log
[error] PHP Fatal error: Class 'Net_SMTP' not found in .../php5/lib/php/Horde/Mail/Transport/Smtp.php on line 271, referer: http://webmail.example.com/imp/compose-dimp.php?type=new&ajaxui=1&uniq=13123591417264
So I checked the Smtp.php file and I saw that the Net_SMTP class is required
* SMTP implementation.
* Requires the Net_SMTP class.
To install the Net_SMTP with PEAR you have to
pear install Net_SMTP
After this procedure I was able to send mail through my smtp server.