On 4 Dec 2006 at 10:03, [log in to unmask] wrote:

>Lately I have been seeing the following error messages for several
>subscribers on our ListServ. The emails do not seem to match up and I am
> 
>Err First Last Address
>--- ----- ----- -------
>1 11/29 11/29 [log in to unmask] Last error: smtp;550 5.7.1 Unable
>to deliver to <[log in to unmask]>

According to RFC1893:

X.7.1   Delivery not authorized, message refused

   The sender is not authorized to send to the destination.
   This can be the result of per-host or per-recipient
   filtering.  This memo does not discuss the merits of any
   such filtering, but provides a mechanism to report such.
   This is useful only as a permanent error.