Reverse address cache size and reverse address cache timeout MTA options

LDAP lookup cache MTA options:  (integer) and    (integer)
The  MTA options control some performance tuning relevant when operating in direct LDAP mode, in particular when the   MTA option is set. When such  address reversal LDAP lookups are performed, the results can be cached; that is, an in-memory cache is maintained of the results of "recent" such lookups. The  option, which defaults to 100000,  controls how many results are cached. The   option, which defaults to 600, specifies how long in seconds to maintain cache results. There is a trade-off between performance on the one hand, vs. memory usage and speed with which changes to the LDAP entries take effect on the other hand.

See also:
 * LDAP lookup cache MTA options
 * reverse_url MTA Option