3.34. How do I spoof-proof my one-way (announcements or newsletter) list?

If you've had problems with virus-generated messages with spoofed senders getting through to a one-way list (we have), you can completely spoof-proof your list by requiring Web-based approval of every message even if it is sent by the list's moderator (the author, in case of a one-way newsletter).

Under Privacy Options, Recipient Filters, set max_num_recipients to 1. This will cause every message posted by the moderator to require approval via the Web (Reason: too many recipients)

You must also set require_explicit_destination is set to "yes" to preclude allowing a post with zero recipients (i.e. list in Bcc:).

Q: One? Don't you mean zero?

No. Its definition is "If a posting has this number, or more, of recipients, it is held for admin approval. Use 0 for no ceiling."

As noted in article 3.11 (see How do I create a newsletter, announcement, or one-way list?), the secure way to do this is to set everyone's moderation bit on and set the default for new subscribers to moderated and post using an Approved: header. This way, no one can post directly to the list without a header of the form

Approved: <password>

in either the headers or the first body line of the message. The header is of course removed before the post is delivered to the list.

In the above, <password> is the list's admin, moderator, or (in 2.1.15 and up) poster password.

The Approved: header would also work to pre-approve posts if all messages are held via set max_num_recipients = 1, but moderation of members offers more options than just holding posts.

Converted from the Mailman FAQ Wizard

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