Question : ESMTP #550 Mailbox unavailable or access denied -  <emailchanged@outsideourdo<wbr />main.com> ##

We are in the middle of migrating from exchange 2003 to exchange 2007.  I have the new box completely built out and the admin account and myself moved onto it.  All replication is set up.  We have the rest of the 100 users still on the old 2003 box.  Ever since we brought it online we are getting some random messages about return emails we are sending out, by random I mean sometimes they go through sometimes they do not.  These are good email addresses, and we have had no problem mailing out to them before bringing up the new box.  There are a number of different errors but most of them start out like this:

Delivery is delayed to these recipients or distribution lists:
RECIPIENT HERE
Subject: test
This message has not yet been delivered. Microsoft Exchange will continue to try delivering the message on your behalf.
Delivery of this message will be attempted until 7/3/2008 10:15:06 AM (GMT-07:00) Mountain Time (US & Canada). Microsoft Exchange will notify you if the message can't be delivered by that time.

Then we get this error a little while later as an email to the sending user:

Delivery has failed to these recipients or distribution lists:
username@outsideourdomain.com
An error occurred while trying to deliver this message to the recipient's e-mail address. Microsoft Exchange will not try to redeliver this message for you. Please try resending this message, or provide the following diagnostic text to your system administrator.
The following organization rejected your message: ESMTP.
________________________________________
Sent by Microsoft Exchange Server 2007




Diagnostic information for administrators:
Generating server: fqdn2007exchangeserver.ourdomain.com
usernamechanged@outsideourdomain.com
ESMTP #550 Mailbox unavailable or access denied - rdomain.com> ##
Original message headers:
Received: from fqdn2003exchangeserver.ourdomain.com (internalIP) by
 fqdn2007exchangeserver.ourdomain.com (internalIP) with Microsoft SMTP Server id
 8.1.278.0; Mon, 30 Jun 2008 09:38:33 -0600
X-MimeOLE: Produced By Microsoft Exchange V6.5
Content-Class: urn:content-classes:calendarmessage
MIME-Version: 1.0
Content-Type: multipart/alternative;
      boundary="----_=_NextPart_001_01C8DAC7.5AC0BC87"
Subject: Introductory capabilities discussion
Date: Mon, 30 Jun 2008 09:38:33 -0600
Message-ID: <1564E15C3F67AA46A77C681B6D13717B0B1BFB@fqdn2003exchangeserver.ourdomain.com>
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
Thread-Topic: Introductory capabilities discussion
Thread-Index: Acjax1o5/IeD8PyqQ4a4Asv7WzCkuAAAAAog
From: Username
To: Username , rdomain.com>
Return-Path: [email protected]

All I can think of is the connector has some sort of issue, wherein the 2003 server originates the email, kicks it to the 2007 server (for some reason I do not know) and then the hub looks to see what has lowest priority. If the 2003 server is busy the 2007 server tries to send it out itself.  So I went in and made the 2007 cost to 50, but we are still getting the random rejected messages.  The error code does not even address another server outside our domain, so I have to assume that the message is dying at the 2007 server.  

Any ideas would be greatly appreciated.  By the way, this is my first post to this board, so if I didn't format it properly or made a mistake somewhere, please forgive me and let me know what I need to do for future reference.

Thank you,
Affl1ction

Answer : ESMTP #550 Mailbox unavailable or access denied -  <emailchanged@outsideourdo<wbr />main.com> ##

It could be that the error is due to not having reverse DNS configured for your new server. If that is the case, there may be several mail servers that will not respond to request or reject them altogether. It is common with providers like Comcast, AOL, etc.

In this case, if you didn't have reverse DNS set up (or getting any other error similar for that matter), Exchange 2007 is designed to give you an ambiguous response that "appears" to be coming from your internal server. Which would likely make you believe that there is something wrong with the connector or an internal bug with Exchange.

Try running a telnet session from your new Exchange 2007 server to the email domain that you are getting the error from and see if you get the same response from the server on their end? I'm betting to guess that you probably do and even though the error is coming from their server, Exchange 2007 notifies you of the error and it makes it appear like it's coming from your internal server. (Don't ask me why MS decided to do that...).

We ran into the same situation and I was just trying everything under the sun to figure it out. I tried this simple test and surprisingly I got the error response from the external mail server. In any case, I set up reverse DNS for my new server (even though I only needed it for a short period during transition) and everything seemed to work beautifully.

Hope that helps...
jphifer