#550 5.1.1 RESOLVER.ADR.RecipNotFound

When I try to send an email to an external address (different domain), my Exchange 2007 Server replies with the NDR below. I can send to other recipients at that external domain, just no to this specific user. I am also not able to send it from OWA.  Any Ideas?

Thanks in advance



Diagnostic information for administrators:
Generating server: MyDomain.COM
USER@OtherDomain.com
#550 5.1.1 RESOLVER.ADR.RecipNotFound; not found ##
Original message headers:
Received: from MyDomain.COM ([fe80::3842:f81e:b98:ffb4]) by
 MyDomain.COM ([fe80::3842:f81e:b98:ffb4%10]) with mapi; Fri, 1 May
 2015 07:56:53 -0800
Content-Type: application/ms-tnef; name="winmail.dat"
Content-Transfer-Encoding: binary
From: Tracy Thomas <Sender@MyDomain.com>
To: "USER@OtherDomain" <USER@OtherDomain>
Date: Fri, 1 May 2015 07:56:52 -0800
Subject: test
Thread-Topic: test
Thread-Index: AdCEJ2/cH6f2ja69QL6apvN2g4yppg==
Message-ID: <558C49C134BA9340B71221CC29728ED1925E54D36A@MLA03.MAPPINGALASKA.COM>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator: <558C49C134BA9340B71221CC29728ED1925E54D36A@MLA03.MAPPINGALASKA.COM>
MIME-Version: 1.0
mapalaska2003Asked:
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Michael MachieFull-time technical multi-taskerCommented:
It looks like it is something as simple as the address (on that domain) is not a legit address. For instance, if you are trying to email Pault@domain.com but Paul's address is actually ptuttle@domain.com, you will get that message. You would still be able to send emails to that same domain but the individual's address is not correct.

To fully identify if this if you or them, you can call the person and verify the address is correct or send another email from a different email domain to that address and see if it bounces back. If so, it would def be a wrong address issue.  

The message is specifically saying that the particular email address you used is not found on the receiving server.
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mapalaska2003Author Commented:
I verified the address. Something on my server seems to be the problem. Any other ideas?
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Michael MachieFull-time technical multi-taskerCommented:
I also recently had a similar but different issue and discovered it to be related to a TLS 1.0 request that was failing - It was the same exact message.

Someone was sending an email to one of the Domains I support and they kept receiving that message when sending to my supported Domain. It ended up being specific to that one User and was related to a TLS 1.0 request being sent by his email to our Domain and our Domain rejected it.

It was only a single User not within my supported Domain and that person ended up leaving their employment after only a short time. I did nothing about it and have never heard of anything like that from anyone either before, or since. I suppose it could be related to the Server certificate they have on their email Server not supporting a TLS 1.0 request because I heard recently that any Domains with a .local in their internal Domain name (ie/ domainname.local) will have these TLS 1.0 request issues starting this year.

Perhaps that is the problem?
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matrix8086Commented:
You need to configure reverse DNS (an PTR record in the DNS). In some cases this have to be done by the ISP
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Michael MachieFull-time technical multi-taskerCommented:
@matrix8086: Would you please clarify why this would be the case? In my instance we have the PTR record in DNS and still had the issue with someone emailing one of my Domains. I am interested in hearing more about that.
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mapalaska2003Author Commented:
I don't understand why Id need to change anything in the DNS. I can send mail to everyone else at that domain, just this one user is the problem. I've checked the users Gmail account as I have administrative access to it.

I have added the user as a Contact in Active Directory, but that did not work either.
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matrix8086Commented:
I will explain mail + reverse DNS. Every mail server can be configured to check reverse DNS when a message arrives, this is the sysadmin option.

There are spammers who send mail messages in behalf of others. If I am a spammer I will send messages in behalf of good@example.com from anywhere in the Internet, through different hacked or open relay mail servers. But the mail server mail.example.com have only one unique IP address (let's say 11.12.13.14) and there are sysadmins who tell their mail servers: when a message arrive check if the IP is corresponding with real name (this is the reverse DNS which assume a PTR record in the DNS zone). So in this case, when such a mail server receive a message from good@example.com, it checks if 11.12.13.14 -> mail.example.com. If a spammer send an email in behalf of good@example.com from IP 13.13.13.13, the receiving mail server check the IP 13.13.13.13 (in fact it checks at the first moment when sending server ask for connection)  and discover another name, or nothing (I will comeback at "nothing") and drop the connection. Te sending server think that the recipient sever does not respond (is down, don't exist, etc).

But if example.com has no PTR record (no reverse DNS, which means "nothing" from above)  it won't be able to send messages to such mail servers which check for reverse DNS, because the recipient server receive no answer of reverse DNS request (and it is considered spammer even if is not!) - and that could be the case of mapalaska2003.

But if thats's not the case and the user address is correct, then it could be only one problem: the receiver has a big infrastructure with more than one mail server and somehow in that infrastructure the routing path to the user is broken. It can be happening when a user mail database is moved from a server to another or some changes occurs in that infrastructure.

As 550 5.1.1 is described by Microsoft, this last paragraph seems to be the case.

But as I type I know how to check this: if it is a reverse DNS issue, the error is received after a while (by default 4 hours, because the sender don't find the recipient server). If it's a user issue on the other/recipient side, the error occurs in few minutes
 
Best regards!
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mapalaska2003Author Commented:
Thanks for the info Matrix.

I do have some more information however. If I use an email account outside of my domain, it delivers fine (ie: Yahoo).

There are other users on the external domain that can receive it just fine. I created a test account on the external domain and it failed as well.

It's got to be something in my domain / Exchange that's causing this.
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mapalaska2003Author Commented:
I figured it out. Since there are users within my domain that also have email accounts on the external domain and use Outlook for both accounts. I had to add the external user as a Mail Contact in Recipient Configuration in the Exchange Management Console. That took care of it.

Thanks to Both of you.
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Michael MachieFull-time technical multi-taskerCommented:
Nice job geting to the bottom of it.
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