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Email NDR Help needed- #4.3.2 smtp;451 4.3.2 / #4.7.1 smtp;450 4.7.1

Lately we have had some issues with NDR's on emails sent out a couple of weeks ago.  Here are two returns we saw.
1.  Your message did not reach some or all of the intended recipients.

      Subject:      Rules
      Sent:      2/2/2009 2:47 PM

The following recipient(s) could not be reached:

      removed@removed.com on 2/12/2009 12:12 AM
            This message was rejected due to the current administrative policy by the destination server.  Please retry at a later time.  If that fails, contact your system administrator.
            <removed.removed.com #4.3.2 smtp;451 4.3.2 Please try again later>

2.  Your message did not reach some or all of the intended recipients.

      Subject:      FW: AT&T Account
      Sent:      1/26/2009 8:22 AM

The following recipient(s) could not be reached:

      removed@removed.net on 2/12/2009 12:11 AM
            You do not have permission to send to this recipient.  For assistance, contact your system administrator.
            <removed.removed.com #4.7.1 smtp;450 4.7.1 <removed@removed.net>: Recipient address rejected: Greylisting in action, please try later>

We have seen a few different domains return messages like these but all other emails go through with no issues.  We are running Windows Server 2003 with Exchange Server 2003.  Please let me know if you need any more information.  Thank you!
1 Solution
Some mail servers are using this temporary error message (non-fatal, so the originator should try again) for Greylisting. The first attempt always get denied.

This is a starnge technique to fight SPAM these days. Ideally SPAMMERS wont retry if they are rejected but geniune mail system does retry. You should look at the recipient system 7 ask them to add you to safe senders list

Here are some links regarding this issue:


Same problem already solved:


post back if you do not find your problem in this.
MNBTechAuthor Commented:
Is it possible that my exchange server is set not to resend the message once the recipient server rejects the first on?  How would I check this?
Greylisting. I use it myself and find it very effective at dealing with about 70% of spam. IMF soaks up the rest.
Unfortunately Exchange has a bug that in some cases it will not try and send the messages again. This has been resolved by a hotfix for Exchange.

As for getting Exchange to bounce the messages back immediately, alas that isn't possible. The NDR is a temporary failure, which means that Exchange will try again. You cannot force Exchange to treat temporary failures as a permanent one.

MNBTechAuthor Commented:
Thank you all for your help so far.  Mestha, I think thus far the information you have provided sounds like it may help the most.  I am downloading the hotfix and I will do some testing.  I will follow up soon.  Other ideas of course are welcome as well.

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