I have a feature request for what might help w/ the external LDAP mapping troubles that see frequent posts here:
Create a GUI external LDAP to Zimbra LDAP mapper in the admin panel setup under either authentication or GAL setup that would do something like:
1) Grab a model entry from an external LDAP search string:
2) Pull in all the published attributes for that entry and give an AJAX mapping screen that lets you configure the zimbra->external LDAP mappings that will be written to the Zimbra LDAP config entries when saved.
Just a thought. I'm new to Zimbra, but am very impressed by it!