Occasionally, people set up mailman lists that are intended to be "one-way" or "announcement" lists that are not properly configured as such (see this FAQ).

They then add a large list of addresses to the list, often without consent or opt-in from those people. Yours is one of those addresses. Then they send something to the list. Several people reply to this unsolicited message with "take me off this list", "unsubscribe" or "stop sending me this" kinds of replies and because of the way the list is misconfigured, these messages are sent out to all the list members. This quickly snowballs with "I didn't send that", "stop spamming me" and worse messages flying everywhere.

The correct response to this situation is to unsubscribe yourself from the list. See the list members manual for help with this.

Unfortunately the GNU Mailman project has no control over the people who do this, and other than providing you with unsubscribe information as in the list members manual, we can't be of much further help.