Zimbra is setup to query addresses from a External GAL. Settings are as follows.

GAL Mode = External
Most results returned by GAL search = 1000
Server Type = LDAP
External Server Name = ldap://192.168.xx.xx:389
LDAP Filter = (|(cn = %s*)(sn=%s*)(gn=%s*)(mail=%s*))
Autocomplete Filter = (|(cn = %s*)(sn=%s*)(gn=%s*)(mail=%s*))
LDAP search base = (O=xxx)

Some addresses in the LDAP are not coming for Autocomplete. But they can be viewed when we click on "To" button and search. What can be the reason that some addresses are not coming for Autocomplete? The Filter is same for LDAP Filter and Autocomplete filter. Thank you.