Unable to Sent to a Particular User

A user suddenly stopped being able to send to an email address that she had previously been able to email to.  The name changed from his "name" to his email address in her address book, but the email address seemed to be the same.  She can send to other external email addresses, but this user gives the following errors in order:

Subject: Test Email
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 10/2/2011 12:00:27 PM (GMT-05:00) Eastern Time (US & Canada). Microsoft Exchange will notify you if the message can't be delivered by that time.


Delivery has failed to these recipients or distribution lists:
Microsoft Exchange has been trying to deliver this message without success and has stopped trying. Please try sending this message again, or provide the following diagnostic text to your system administrator.
Sent by Microsoft Exchange Server 2007

Diagnostic information for administrators:
Generating server: [server].local
#550 4.4.7 QUEUE.Expired; message expired ##
Original message headers:
Received: from [SERVER].local ([fe80::25a6:8b3c:c593:1142]) by
 [SERVER].local ([fe80::25a6:8b3c:c593:1142%11]) with mapi; Fri,
 30 Sep 2011 12:00:27 -0400
From: <[emailaddress]@DOMAIN.us>
To: [emailaddress]@bellsouth.net
Date: Fri, 30 Sep 2011 12:00:26 -0400
Subject: Test Email
Thread-Topic: Test Email
Thread-Index: Acx/ihHBr9ccS31MSxm24HuhTWRcIg==
Message-ID: <84F9AA08195BA74F9A5E9E2490D23A630500D0B080@[SERVER.local]>
Accept-Language: en-US
Content-Language: en-US
acceptlanguage: en-US
Content-Type: multipart/alternative;
MIME-Version: 1.0
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I am hoping that this issue is only to one specific user, if so.. I had the same issue in past and had to remove the mailbox and create new one..

Exporeted all emails to PST and created new one then imported from PST and it resolved the issue..

and make sure the client is not in cached mode, if you want to delete and create new mailbox..

Neil RussellTechnical Development LeadCommented:
1) Have you veryfied that the email address is valid? you can use http://verify-email.org/

2) Can you send from a differnt account?

3) Can you resolve the MX address of bellsouth.net from your mail server correctly?

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Neil RussellTechnical Development LeadCommented:
4) Tried her logging into webmail and sending to that email address?
MedquestAuthor Commented:
Thank you for the responses.  So far I have attempted to verify the email address and gotten:

Result: Bad
Description: 521- blocked by ldap:ou=rblmx,dc=att,dc=net

I tried to send from my account on another domain, but haven't recieved anything back yet, but she states it normally takes a few hours for the return message to come back to her.  
A rejected email from underlivered domain should get almost instantly, If the message is not being transmitted yet you can verify by using the Queue viewer on the Transport server and see if the message is still there.

You can try sending the email to the same recipient with Deliver confirmation and you should get the response once the mail is being delivered.
MedquestAuthor Commented:
I did that and got: "Delivery to these recipients or groups is complete, but no delivery notification was sent by the destination server."
It seems from the descruption you have provied above, domain is in blacklisted.. Can you confirm with you ISP, I believe it is ATT from the log..
MedquestAuthor Commented:
I just received a message that she could not send to another address.  The first email was sbcglobal and the other is bellsouth.  Both are showing up as 'bad' with the email verifier, so my question is, if an email is blacklisted will it prevent you from sending to it?  It seems obvious that you couldn't get email from it, but does it work vice versa?
Both the email addresses belongs to ATT I believe,  Make sure that both addresses are active. I would try sending by other domain (gmail, yahoo etc.. just to verify) and the blacklist is not vice versa, it depends on the service (spam filter) being used.

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