Messages to the list are delivered to a .qmail file, usually ~/.qmail-listname which is linked to DIR/editor. Here, the message is first delivered to ezmlm-reject(1) which can reject messages based on subject line contents, MIME content-type, and message body length. It also by default rejects all messages that do not have the list address in the ‘To:’ or ‘Cc:’ header. This eliminates most bulk spam. If the list is set up for restrictions based on envelope SENDER, the next delivery is to one or more instances of ezmlm-issubn(1). If the messages passed this check, it is usually delivered to ezmlm-send(1) for distribution. If the list is message moderated, it is instead delivered to ezmlm-store(1) which queues the message and sends out a moderation request. ezmlm-gate(1) is used by some other setups. It will for message moderated lists invoke ezmlm-send(1) directly if the message is from a specific set of SENDERs, and in other cases ezmlm-store(1) to send the message out for moderation.
You can specify a separate .qmail-like file for ezmlm-gate(1). The lines will be executed and the return codes determine if the message is rejected, sent to the list, or sent to the moderator. See man page for details.
If the list is configured for digests, DIR/editor also contains an ezmlm-tstdig(1) line followed by an ezmlm-get(1) line. If ezmlm-tstdig(1) determines that the criteria are met for digest generation, it exits with an exit code of 0, causing the ezmlm-get(1) line to be executed leading to a digest mailing. Otherwise, ezmlm-tstdig(1) exits 99, resulting in the remainder of the DIR/editor file to be ignored too long. The digest is not related to the message being delivered, but the delivery is used to trigger execution of the relevant programs.
In addition, DIR/editor contains a number of house-keeping functions. These are invocations of ezmlm-warn(1) to send out bounce warnings and and (if the list is moderated) ezmlm-clean(1) to clean the moderation queue of messages that have been ignored. Again, these functions are not related to the specific message delivered, but the delivery itself is used as a convenient ‘trigger’ for processing.