== How do I respond to a held message notification to accept or discard the message? ==

If the list's General Options -> admin_immed_notify attribute is Yes, when a list post is held for moderator action, a notice is sent to the list's owner and moderator addresses. This email has the following MIME structure:

multipart/mixed
 text/plain
  Information about the held message
 message/rfc822
  A copy of the held message
 message/rfc822
  A message which says:
   If you reply to this message, keeping the Subject: header intact,
   Mailman will discard the held message.  Do this if the message is
   spam.  If you reply to this message and include an Approved: header
   with the list password in it, the message will be approved for posting
   to the list.  The Approved: header can also appear in the first line
   of the body of the reply.

The Subject and From of the outer message are:
{{{
Subject: LISTNAME post from user@example.com requires approval
From: LISTNAME-owner@example.net
}}}
The Subject and From of the second message/rfc822 part are:
{{{
Subject: confirm <a long string of hex digits>
From: LISTNAME-request@example.net
}}}
The key thing here is the text that says "If you reply to this message ..." is referring to the message in the second message/rfc822 part, not the outer message.

This means in particular that in order to work, the reply, with or without the Approved: header must be sent `To: LISTNAME-request@example.net` with `Subject: confirm <the long string of hex digits>` (the Subject: can also be "Re: confirm <the long string of hex digits>". If you reply to the outer message, your reply goes `To: LISTNAME-owner@example.net`, and you just get a copy of your reply sent back to the owners/moderators.

Some MUAs make it easy to reply to a message/rfc822 subpart and some do not, but you don't really need to 'reply'. Sending any message `To: LISTNAME-request@example.net` with `Subject: confirm <the long string of hex digits>` and with or without the `Approved:` header as desired will work.