How do I add a CancelBot to my mailing list?

Some Usenet news groups use a "CancelBot" to ensure that every person who contributes has read the rules of the group, such as what kind of message topics are appropriate.

For example, the alt.comp.hardware.homebuilt News group FAQ explains CancelBots in this way:

Because of excessive noise (mostly involving off topic
"fix my PC" type questions) a cancelbot has been set
up on this newsgroup. Failing to inform the cancelbot
 that you have read the posting rules may result in
your post being automatically canceled. To let the
cancelbot know that you are aware of the posting
rules, you must add the letters "PRR" (without the
quotes) somewhere in your first post. PRR stands for
"Posting Rules Read".

ListManager also supports CancelBots. To implement a CancelBot on your mailing list, you create an Action Phrase on your mailing list that is triggered when a given word or phrase is not present in the message. Thus, any message that does not have the term you specify will be automatically rejected, and the person will receive a document you specify in response.

The first step is to create a document with the posting rules for your mailing list. See "Server Documents".

Then, create an action phrase with the following properties:
 

Phrase: enter the word or phrase you want to have required in all postings

Response: choose the document that should be sent to rejected postings. This is most likely a copy of the posting rules.

Rule: choose "phrase does not appear in the message body". Alternatively, if you want to require the phrase to be in the subject, or to be anywhere in the message, you can choose "phrase does not appear in the subject" or "phrase does not appear anywhere in the message"

Context: choose your mailing list.

See "Site Action Phrases".