Thanks Quanah/Mauricio/Chris for the reply.

In fact, that is the first thing I did, I get the following error when I start ldap service.

Checking configuration files for slapd: bdb_db_open: Cannot access database directory /var/vamail/ldap/mydomain.com (13)
Backend_startup_one: bi_db_open failed! (-1)
Slap_startup failed (test would succeed using the –u switch) [FAILED]
Stale lock files may be present in /var/vmail/ldap/mydomain.com [WARNING]

Permission looks exactly the same. Any idea why this error?