On Tue, 10 Oct 2000 13:31:04 +1100, Michael Shannon <[log in to unmask]>
wrote:

>I know it's a fortnight late but I still have a question about this.  Why
>would an error be generated back to LISTSERV by a forwarding address?
>Wouldn't it be more likely to send an error back to the originating mail
>server and stop there?

[log in to unmask] is subscribed to the list.  USA.Net is a well know mail forwarder
service.  All mail to that address actually is forwarded to [log in to unmask]  

Mail posted to your list goes out with 

RFC822 From: Michael Shannon <[log in to unmask]>
RFC822 To:   [log in to unmask]
RFC822 Sender: [log in to unmask]
RFC821 Return_path:  <[log in to unmask]>
RFC821 RCPT TO:<[log in to unmask]>

Only one of these headers is changed when the mail gets to usa.net and is
forwarded on to [log in to unmask] and that is the RFC821 RCPT TO:<[log in to unmask]>.  All
other address lines remain the same.

If, when mail gets to aol.com,  the account [log in to unmask] is a)mailbox full, or
b)not receiving mail from internet or c)closed/inactive then a Non-Delivery
error will occur.  RFC821 says that error must be reported back to the
Return_path address.  The error message will come From: [log in to unmask] and
be addressed To: [log in to unmask] and will say (in short)

550 no such user
Address: [log in to unmask]

Notice that nowhere is [log in to unmask] referenced in this error report.  

As happens, because an error is reported, this address will show up on the Daily
Monitoring Report, whether or not the address [log in to unmask] is subscribed to your
list (it is not in fact).