I haven’t installed nethserver-horde at any time, I only installed it manually, but perhaps I can help.
At manual steps for horde mail you need to:
Please install mailserver from softwarecenter. After that you have to install imp for webmail and ingo for filtering mails in terminal
yum install php-horde-imp
yum install php-horde-ingo
After installation go back to X.X.X.X/horde/admin/config at your browser and click on horde.
Possible messages about DB Shemas you can ignore at this time.
Go to mail tab and setup the following values:
$conf[mailer][type] SMTP server (HIGHLY RECOMMENDED)
$conf[mailer][params][host] smtp.YourDomain
$conf[mailer][params][port] 587
$conf[mailer][params][secure] tls
$conf[mailer][params][localhost] YourDomain
$conf[mailer][params][auth] Yes
$conf[mailer][params][username] admin@yourDomain
$conf[mailer][params][username_auth] true
$conf[mailer][params][password] YourPassword
$conf[mailer][params][password_auth] true
$conf[mailer][params][lmtp] false
Now we can go to IMAP Server tab and set the following values
$conf[imap][enabled] Enabled
$conf[imap][server] imap.YourDomain
$conf[imap][port] 143
$conf[imap][secure] tls
$conf[imap][maildomain] YourDomain
$conf[imap][cache_folders] true
Now press the button to generate the Horde configuration again.
We have to create a webmail configuration now, click at Webmail (imp). If you want you can change some values here.
If you have finished, click on generate Webmail-Configuration.
After that you have to Update All DB Schemas.
For that you have to click “Update All DB Schemas” at X.X.X.X/horde/admin/config.
Now you can use the mailsystem. Your mail-adress is the one from active directory.