If you're using Direct LDAP lookups the following parameters should be set in option.dat:

Note: If you're using iMS 5.2 or later then YOU SHOULD BE USING Direct LDAP, instead of Dirsync!

To get the maximum gain from DirectLDAP Mode, you should also look at adjusting MAX_LIFE_CONNS see Section 8.1 for more information.

ALIAS_ENTRY_CACHE_SIZE -- this is the maximum number of entries held in the cache. The default value is 1000. Each cache entry is about 2K.

ALIAS_ENTRY_CACHE_TIMEOUT -- this is the maximum length of time, in seconds, an entry is held in cache, the default value =1200

ALIAS_ENTRY_CACHE_NEGATIVE -- controls if alias match failures are cached. The default action is not to cache failures. This speeds up the activation of new users.

DOMAIN_MATCH_CACHE_SIZE=50

DOMAIN_MATCH_CACHE_TIMEOUT=60000