At the most basic level it means a message which appeared to be from, or
related to, your list, was rejected by the mail server for the
destination domain.

If the listed email address is not subscribed to your list, then it may
mean that some spam got through the various incoming filters and
LISTSERV processed it.  In this case the error should not recur, so if
the error count does not change on your next daily report you may safely
ignore it.  Address harvesting methods used by spammers sometimes yield
incorrect results - such as combining nearby text with the address (like
the "6" in the example you gave).

If the error count increases, I would say ask the list host site
administrator to investigate.

Do you have any legitimate subscribers on the list from that domain? If
so, perhaps ask the administrator there to look into this situation.


On 2/23/2011 8:21 AM, Eric Johnson wrote:
> 1 02/22 02/22 [log in to unmask]
>                  Last error: 5.1.1 550 5.1.1<[log in to unmask]>: Recipient
>                              address rejected: User unknown in relay recipient
>                              table
>
> I had 20 errors last night of this type. Same domain but different addresses and
> the addresses seem to be in hex.
>
> Eric Johnson
> Toller-L