[richardcwgate]

Here's what you need to do to get Joomla to authenticate via Zimbra LDAP.
I assume Zimbra is enabled for ldap on port 389.
1) Create a Joomla account eg. with name myusername
2) Create a Zimbra account with the same name
4) Configure the Jooma ldap authentication plugin;
Enabled - Yes
Host - the FQDN for your Zimbra server
Port - 389
LDAP V3 - Yes
Negotiate TLS - No
Do not follow referrals - No
Authorization Method - Bind Directly as User
Base DN - dc=servername,dc=com (or what ever you use)
Search String - leave blank
Users DN - uid=[username],ou=people,dc=servername,dc=com (or what ever you use)
Connect username - leave blank
Connect password - leave blank
Map: Full Name - fullName
Map: E-mail
Map: User ID - uid
5) Make certain that the Joomla and Zimbra accounts have different passwords, then you know which authentication you have used.