The IMTA runs a periodic job called post.sh every four hours. The post.sh program scans through all the channels currently defined in the configuration file and checks the corresponding queues for messages. Processing jobs are unconditionally submitted to run the master channel programs for any channels, with master programs so as to poll remote systems that cannot establish their own connections. Jobs are also submitted for channels that support master channel programs and have messages queued. After this is done post.sh then terminates. It will run again in another four hours.
post.sh, is the shell script /opt/SUNWmail/imta/lib/post.sh, which the cron daemon is normally scheduled to run every four hours. IMTA's suggested default behavior of running the periodic delivery job once every four hours is appropriate for most sites. Indeed, at busy sites, running the periodic delivery job too frequently tends to be counterproductive.
If a site has a special need to run post.sh more frequently, they can change the crontab. Note, however, that RFC 1123, Requirements for Internet Hosts, requires that Internet mail wait at least 30 minutes before being retried. Do not run your channel to the Internet more frequently than every half hour.
Finally, IMTA normally performs some periodic clean up tasks when post.sh runs. IMTA's defaults are tuned for the case where the periodic job only runs every couple of hours. If you will be running the periodic job more frequently, you should adjust IMTA's clean up task frequency: the IMTA_SYNCH_CACHE_PERIOD and IMTA_VERSION_LIMIT_PERIOD IMTA tailor options should be set to integer values so that these tasks are still performed only every couple of hours or so. (Refer to SIMS Reference Manual for more details on these strings.)