I am trying to accomplish an objective, I need to get 389 Directory server installed
in the process however is it possible to just have email addresses of users
in the LDAP server?

I have a primary domain, example 'abcefg.com' with about 3,000 users and
several hosted domains like 'xyz.com' and 'mno.com'.

The end goal is to speed up email processing, so instead of the Barracuda asking
the email server(s) if a user exist it queries the LDAP.

Is there a way to configure 389 Directory Server to contain just the email
addresses of the end users to allow the Barracuda to poll the LDAP server to
verify the email address is valid. The rest of the authentication like password
is handled by the email server.

So in the end the LDAP server would just contain the email addresses (live) and the
Barracuda would query the LDAP asking if joebob@abcefg.com exist if it does carry on.
If user xxeedd@abcefg.com does not exist drop it and go on.

Any ideas or help would be greatly appreciated.

thanks

The data in the directory really has nothing to do with the directory. It's just data. If you use an inetorgperson object, then that contains an email address attribute, but you can in principle put your arbitrary data string wherever you want.

If this is a sompletely new thing to you, i'd probably suggest using openldap instead, it's easier to get going with, and 389DS is really fairly clunky old code that's but whored around a number of different companies over a decade, and ... eurgh.

Would you suggest just using openldap that is available in the channel, just use yum install openldap (ect...)?

It's what i'm using professionally, yes. BUT if you want tui do replication you should actually look at version 2.4 which has a much better replication model than 2.3 which rhel 5 uses.