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:

uid=joeuser,dc=company,dc=com

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!