Alias_entry_cache_* MTA options
LDAP and URL lookup cache options:
alias_entry_cache_negative (0 or 1),
alias_entry_cache_* MTA options control some performance tuning relevant when operating in direct LDAP mode, in particular when
alias_urlN options are being used. When
alias_urlN lookups are performed, the results can be cached; that is, an in memory cache is maintained of the results of "recent" such lookups. The
alias_entry_cache_size option, which defaults to 1000, controls how many results are cached. The
alias_entry_cache_timeout option, which defaults to 600, controls how long in seconds to maintain cache results. The
alias_entry_cache_negative option, which takes a boolean argument and defaults to 0 (false), controls whether or not negative results (that is, failures to find an alias) are cached.
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.