Recipient email servers looking for source domain entry??

[Mathias Koerber]

On Sun, 5 Mar 2000, Jim Picerno wrote:

| Date: Sun, 5 Mar 2000 19:55:09 -0800
| From: Jim Picerno <jpicerno at speakeasy.org>
| To: comp-protocols-dns-bind at moderators.isc.org
| Newsgroups: comp.protocols.dns.bind, microsoft.public.windowsnt.dns
| Subject: Recipient email servers looking for source domain entry??
| 
| I'm using Exchange 5.5 and I'm gettng the error messages I've listed below.
| Are these errors referring to a specific DNS entry or is it some other
| problem with DNS. If there is a specific DNS entry could someone provide an
| example?

The first. Many mailservers these days expect that the sender (SMTP MAIL FROM)
use an existing domain, so that errors etc can be sent back. FOr this
they perform the usual MX (and A) record lookups.

While the initial intent for this may have been to just ensure that errors
during the delivery can actually be sent to the originator, it is often used
as a means to filter non-existent (and thus likely forged) addresses
used in SPAM.

Note that the error you received below is a 4xx error, and thus temporary. This
usually means that the mailserver was not able to verify the domain
(due to network problems etc) and that the sending system (yours) should
retry sending the same mail again later. Had it received an authoritative 'domain does not exist'
from the DNS lookup, it would (likely) have returned the mail with a 5xx (permament) error.

HTH
HAND

| 
| 
| Event Type: Warning
| Event Source: MSExchangeIMC
| Event Category: SMTP Interface Events
| Event ID: 4030
| Description:
| The following message could not be delivered to <Jane_Doe at Destination.com>
| Delivery will be retried later. The  destination server reported: 450
| <John_Doe at Source.com>: Sender address rejected: Domain not found From:
| <John_Doe at Source.com> Subject: ABC123
| 
| Event Type: Warning
| Event Source: MSExchangeIMC
| Event Category: SMTP Interface Events
| Event ID: 4090
| Date:  3/5/2000
| Time:  4:12:52 PM
| Description:
| Mail could not be delivered to 123.456.789.10 (Destination.org). The
| destination server reported 451 <John_Doe at Source.com>... Sender domain must
| resolve. Delivery will be retried later.
| 
| 
| 
| 

Mathias Koerber	  | Tel: +65 / 471 9820    |   mathias at staff.singnet.com.sg
SingNet NOC	  | Fax: +65 / 475 3273    |            mathias at koerber.org
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