On most types of moderated lists, this is the moderator's primary duty. Messages submitted to the list for posting are sent for moderation so that a moderator can select those that enhance the quality of the list content because they are most relevant or interesting to the list community. Conversely, a moderator can reject messages that are inappropriate and return them to the sender, optionally adding comments.

Depending on the configuration of the list, all posts may be moderated or posts from some users may be moderated while posts from others are sent directly to the list. There are three different configurations, two where all posts are moderated and one where posts from the public are sent for moderation but all others can post directly. For more information, see List types with message moderation.

If the list is large or the public is allowed to submit posts for moderation, there may be many more moderation requests than moderators have time to review. The software has a feature that helps relieve this situation: messages that aren't moderated eventually timeout, are automatically removed from the queue and returned to the sender wrapped in a notification message.

On lists that serve smaller groups where posts from subscribers or moderators are sent for moderation, moderators may have to act on a greater percentage of messages in the moderation queue, and moderate the messages more promptly. Users within an organization have a higher expectation of being able to post to the list than the public does, and their posts may contain time-sensitive information.

The Poster List is only used for lists that send public posts for moderation but allow subscribers and moderators to post directly. A moderator uses it to grant select public users the privilege of posting directly to the list by adding the user's email address to the Poster List (a.k.a. Allow List). Since the mailing list only knows a sender by email address, and classifies all unknown addresses as 'public', the Poster List is a great way to add alternate email addresses of known users, or addresses of other non-subscribers who are known and trusted by the moderator. The Poster List is handy but should not be used indiscriminately because users designated as posters retain direct posting privileges until they are removed from the Poster List.

For instructions, see Adding a poster.

Moderator is the most privileged type of list user and a moderator can always post messages to the list. On lists with the strictest control over the content of messages posted to the list, only moderators are allowed to post and all posts are sent for moderation. If you are moderating this type of list, your primary responsibility will be to post messages, then approve your message as it comes through the moderation queue.

Subscription moderation isn't implemented by any of the default list types, but it can be used on customized lists (although it is rare). If your list is configured to accept subscription requests by email but send them for moderation, your responsibilities may include approving or rejecting subscribe and unsubscribe requests as well as moderating messages for posting. As with other email in the moderation queue, if you ignore a subscription request, it will go away. Since this only applies to customized lists, further description of subscription moderation process is outside the scope of this document. A subscription moderation message will provide complete instructions.

For each message sent to the moderation queue, the mailing list sends a moderation message to every email address on the Moderator List. A moderator can act on the message by replying to the email. The list software prefills these fields so that replies function as email address commands. When the list receives a reply from a moderator, it immediately executes the command on the message in the queue and rejects it or forwards it to the list, then deletes the message from the moderation queue.

If a list has more than one moderator, a moderator may attempt to approve or reject an email that has already been acted upon by another moderator. When this happens, the mailing list software returns a failure message to the second moderator. Once a message has been acted on and removed from the queue, no further action can be taken on it, so if you have a strong opinion about whether a message should be approved or rejected, it's a good idea to act on it promptly.

If messages in the moderation queue are ignored, they eventually go away. To minimize the time and effort required to moderate a list, you can selectively moderate deserving messages and ignore all others. Sometimes messages deserve attention because they should be approved, and sometimes they deserve attention because they need to be rejected to prevent another moderator from inadvertently approving them, such as when a user who has proven trustworthy in the past unexpectedly posts something inappropriate. The sender is notified when a message times out in the queue.

The moderation message is cleverly constructed with prefilled 'From', 'Reply-To' and 'Cc' header fields, which contain email address commands. These fields aren't necessarily visible when viewing the moderation message because some of them are in the envelope header, which is usually hidden.

Each of these email addresses is a different mailing list command. The moderator tells the mailing list how to handle a moderation message by sending the moderation message to the 'accept' or 'reject' address. To add the sender's email address to the Poster List (a.k.a. 'Allow List'), the moderator also Cc's the 'allow' address. When the list receives the moderation message from the moderator, it executes the command on the message. Once the list receives an email address command, it manages all the details of posting the message to the list or rejecting it, so moderators do not need to include a copy of the original message. Moderators do have the option of adding a comment to messages they've rejected.

Depending on the moderator's MUA, sending a 'reject' command may be as simple as clicking 'Reply', because most MUAs automatically insert the 'From:' address of the moderation message into the 'To:' field, which rejects the message. Replying to the sender usually inserts the 'Reply-To:' address into the 'To:' field, which approves the message. Using the 'Reply to all' option usually approves the message and also sends a command to the 'CC:' address, which adds the address to the Poster List.

These commands will appear in the body of the moderation message, as shown in the Sample moderation message.

In the following sample moderation message:

To accept a moderation request, select the message, then click 'Reply' or whichever reply method automatically inserts the right email address command into the 'To:' field. If this doesn't work on your MUA, paste the 'accept' email address command into the 'To:' field. Once the moderation message is correctly addressed, it is ready to send. The address in the 'To:' field should look something like this:

In this example, 'listname' is the name of the list and 'example.org' is the domain of the organization's web site.

To reject a moderation request, select the message, then click 'Reply to Sender' or whichever reply method automatically inserts the correct email address command into the 'To:' field. If this doesn't work on your MUA, find the 'reject' email address command in the instructions in the moderation message, then copy and paste the 'reject' address into the 'To:' field. When rejecting a message, the moderator has the option of adding a comment. If you wish to add comments explaining the reason for the rejection and possibly some advice that might be of use to the sender when submitting any future posts, insert your comments between the two marker lines that begin with three percent signs ('%') in a series:

These marker lines are shown in the Sample moderation message.

On most lists, particular those that allow the public to submit messages for moderation, rejection of a message is entirely at the moderator's discretion and the moderator's decision is final and needs no explanation unless the moderator wishes to provide it. This may even be stated explicitly in the lists' Policy and Usage statement. Some lists tend to be more generous with comments because it serves the purposes of the list and the list community. For instance, a moderator might provide a sender with a link to the mailing list's Policy and Usage statement on the mailing list home page to educate an inexperienced sender who has run afoul of formal list policy.

Once the moderation message is correctly addressed, it is ready to send. The address in the 'To:' field should look something like this:

A message that sits in the moderation queue for too long will time out. The length of time it can sit in the queue before timing out is configurable, so you will have to ask a list administrator how your list timeout is set. The minimum timeout is 24 hours, the average is 5 days (120 hours) and the maximum is 10 days (240 hours). When a message times out, it is removed from the queue and the sender of the message is notified (unless the list is configured not to send this notification).

Add an email address command in the following format to the 'Cc:' field: 'listname-allow-tc.messageid-username=example.com@example.org'. The moderation message will contain the actual command for you to copy and paste into this field.

On many MUAs, the 'Reply to All' option automatically fills the 'To:' and 'Cc:' fields with the correct email command addresses, and accepts the sender's email for posting while simultaneously adding the sender's email address to the Poster List.

If you attempt to moderate a message that has already been removed from the queue because it timed out or was acted upon by another moderator, you will receive an ezmlm failure message that contains a description of the error.

When a message is removed from the moderation queue, a stub is stored that indicates the action that was performed on the message. If a moderator sends a moderation message to the list with an email address command, and the message is no longer in the queue, the list will find a stub instead. It checks the stub to see whether the new command is the same as the action already performed on the message.

If they are the same, no further action is taken and the second moderator will not be notified. However, if no stub is found or the second moderation command and the action performed on the message do not match, a notification is sent to the second moderator.

The error message will appear after the phrase 'ezmlm-moderate: fatal', meaning the error condition is permanent—once a message has been removed from the moderation queue it cannot be retrieved. In this excerpt from a moderation failure message, a moderator tried to accept a message that had already been rejected by a different moderator: