This configuration option is used most often when the list owner knows exactly who should be on the list and does not want to be bothered with subscription requests from those who may just be curious about the list's activities. For example, if the purpose of the list is to distribute, say, a monthly newsletter, the list owner is usually not interested in promoting a discussion within the list. If the list owner wants to promote discussion and exchange of ideas, then the list can be configured so that any list member can send a message to the list. While it is possible to configure a list so that non-members can send messages into the list, it is generally not recommended that this option be turned on. Spamming is considered the junk mail of the e-mail world.
Lists can be lightly or highly moderated, depending on the moderator and topic.
In most cases, moderators simply forward messages to the list unchanged. However, the moderator does have the option of summarizing long messages or not forwarding messages on topics that have, say, been exhaustively discussed. Since moderators may be acting as editors, they should take care to represent the original author's message fairly. In digest mode, individual messages that would normally be sent out as they are received are combined into a single message and sent out only once. Owners should keep these guidelines in mind when posting time-sensitive material.