We are implementing LDAP (Fedora Directory Services) with Red Hat Enterprise 4.x everything it's working great except Zimbra and the problem was the following:

The Default domain - zimbra.mycompany.com - we use Internal auth for it.
We add another domain - mycompany.com - we use LDAP External auth with:
- ldap://ldap1.mycompany.com - 389
- LDAP filter: uid=%u
- LDAP Search base: dc=mycompany,dc=com
- Use DN/Pass to bind External Server = Yes
- Bind DN: cn=Directory Manager
- Bind Password: XXXXXXX

In the test part we use and active user in the External LDAP
- user: username (without @)
- pass: xxxxx

And the test it's successful

After that I try to login by webmail client

http://mycompany.com - try to login without success

With the admin account I can login great but with the LDAP External Users DB not. Including I change the user in the test part and work great. Any idea why it's not working!!