My Zimbra server needs to connect to an external LDAP server for authentication. However, the LDAP server requires a trusted CA to connect to it. Where on my Zimbra server should I put the certificate of the external LDAP server? On my other regular Apache website which uses that LDAP authentication, I put the following two lines to httpd.conf:

LDAPTrustedCA /path/to/certificate_of_thatldapserver

And the authentication works for me!