> I was wondering if it would be possible for Listserv to at least check
> for permission to post during the incoming SMTP connection, and perhaps 5xx
> reject the message after the RCPT TO: if the sender is not allowed to
> post to the list.  The error could read something like
>
>   554 5.7.1 Sender not authorized to post to <LISTNAME>

This determination can only be made once the message has been received, which is not the case when processing the RCPT TO: statement. Another obstacle is that LISTSERV does not receive incoming mail over SMTP, this is handled by an external agent that is typically called once the message has been received. As a list owner, I also would not want to reject postings from subscribers with a terse SMTP message. This could be a spammer but it could be my best customer posting from a cell phone with a different address than usual. If the SMTP server could guarantee that it is not a live human being, I would not mind the terse message of course, but there is no way to determine that.

  Eric