Thanks, Ben, et al, for your responses both on- and off-list.

On Mon, 17 Jun 2019 20:13:54 -0600, Ben Parker <[log in to unmask]> wrote:

>This is a bad address.  WHEAETON.EDU is clearly a mis-spelling so Postfix
>should format a proper 'bounce' message and email that back to LISTSERV.

Amen.

>It looks like Postfix is not sending a proper bounce message back to
>LISTSERV for this problem.  As suggested by someone else, you should
>communicate with the LISTSERV Admin about this.

I have verified via tcpdump that the 450 error is being sent back to Listserv.  Is there a way I could see what Listserv is doing with that bounce message when it receives it?

>The SMTP sending part of LISTSERV (under unix) is rather 'simple minded' and
>is basically a 'send and forget' engine.  It is not prepared to handle a 450
>refusal during the transaction.  If Postfix would accept all mail from
>LISTSERV unconditionally (i.e. without trying to validate the destination
>domain during acceptance from LISTSERV, which is what it appears to be doing
>in this case) and then later, when trying to deliver to the non-existant
>domain, if Postfix would then format a proper 'bounce' message with
>appropiate error codes and send that back to LISTSERV, then LISTSERV
>can/will properly deal with the bad address.

If I can make things work as you describe, I would be overjoyed.

Slightly off-topic, but do you (or does anybody) know how to configure Postfix so that it will "accept all mail from LISTSERV unconditionally" and still send the bounce message back to Listserv?

Thanks!

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