The delegateldap Cyrus SASL plugin allows you to forward SASL requests 
from server (like a SMTP or POP server) to a willing OpenLDAP server.

The server that the delegate server is installed on does not need 
access to the OpenLDAP server's passwords. The OpenLDAP server must 
have SASL authentication installed, configured and working 
corretly.

You'll notice that the delegateldap plugin library does not live in 
this directory. It is not loaded automatically by Cyrus SASL. Instead
you must load it explicitly in the sasl config file for the service
that you are authenticating.

Add lines like this to that service. 

# The plugin_list file is *very* fragile, like much of cyrus-sasl
plugin_list: @LIBDIR@/sasl2/delegateldap.sasl
delegateldap_uri: ldap://ldap.example.com/
delegateldap_tls: no