By setting the ForkEachJob ( Y) option, sendmail will fork before each individual message while running the queue. This will prevent sendmail from consuming large amounts of memory, so it may be useful in memory-poor environments. However, if the ForkEachJob option is not set, sendmail will keep track of hosts that are down during a queue run, which can improve performance dramatically.
If the ForkEachJob option is set, sendmail can not use connection caching.