Users regularly send emails to users on another domain. For the past week, some work and some get bounced with 550 5.1.1 message.

I've been able to reproduce the problem sending emails to the same users. Some work some don't. Also, ALL emails are valid - I can send to via another external email.

It looks like (to me) that our exchange 2013 is rejecting some email address and not others. Heres copy of bounce back message:-

Delivery has failed to these recipients or groups:
'user1.thomas@externalcompany.gov.uk' (user1.thomas@externalcompany.gov.uk)
The email address you entered couldn't be found. Please check the recipient's email address and try to resend the message. If the problem continues, please contact your helpdesk.


Diagnostic information for administrators:
Generating server: ourexchange2013.mydomain.gov.uk

user1.thomas@externalcompany.gov.uk
Remote Server returned '550 5.1.1 RESOLVER.ADR.RecipNotFound; not found'

Original message headers:
Received: from ourexchange2013.mydomain.gov.uk (10.94.1.23) by
 ourexchange2013.mydomain.gov.uk (10.94.1.23) with Microsoft SMTP Server (TLS) id
 15.0.1104.5; Thu, 3 Sep 2015 11:32:52 +0100
Received: from ourexchange2013.mydomain.gov.uk ([fe80::1544:60d5:9d27:355e]) by
 ourexchange2013.mydomain.gov.uk ([fe80::ed5f:a121:a3c4:4c61%16]) with mapi id
 15.00.1104.000; Thu, 3 Sep 2015 11:32:51 +0100
Content-Type: application/ms-tnef; name="winmail.dat"
Content-Transfer-Encoding: binary
From: "WILLIAMS, Paul" <Paul.Williams@mycompany.gov.uk>
To: "'user1.thomas@externalcompany.gov.uk'" <user1.thomas@externalcompany.gov.uk>,
"jones,user2" <user2.jones@externalcompany.gov.uk>
Subject: RE: test email from support at abc
Thread-Topic: test email from support at abc
Thread-Index: AdDmMjYoYXi4KIC2Ra2P4rMbdBIg+wAAZbPw
Date: Thu, 3 Sep 2015 11:32:50 +0100
Message-ID: <a21fbbfe27c44d0d94c0b28cb191307a@ourexchange2013.mydomain.gov.uk>
References: <707c69d763274b00bbc53222c02f284f@ourexchange2013.mydomain.gov.uk>
In-Reply-To: <707c69d763274b00bbc53222c02f284f@ourexchange2013.mydomain.gov.uk>
Accept-Language: en-GB, en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator: <a21fbbfe27c44d0d94c0b28cb191307a@ourexchange2013.mydomain.gov.uk>
MIME-Version: 1.0
X-MS-Exchange-Transport-FromEntityHeader: Hosted
X-Originating-IP: [10.90.6.52]
Return-Path: Paul.Williams@mycompany.gov.uk

Only difference seems to be the way users are listed in the message above.  One that works user2.jones.

• Edited by paulfoel 18 hours 4 minutes ago

Hi ,

Below mentioned error message will come in the following situations .

Error Message : 550 5.1.1 RESOLVER.ADR.RecipNotFound; not found

1.you have added the smtp domain name "externalcompany.gov.uk" as authoritative domain in exchange and by not having the mail enabled contacts or mailbox for the users who belongs to that smtp domain suffix i.e (externalcompany.gov.uk") .

2.In few cases autocomplete cache in outlook will create such kind of issues.So for anyone of the affected user please flush the autocomplete cache in outlook and check the results .

By analyzing the error message i came to know that your exchange server 2013 is looking for the recipient (user1.thomas@externalcompany.gov.uk) in exchange and it not available because of that it is giving the bounce back error message to the sender.

Note : On your post you have mentioned that the bounce error is coming for you .So i would suggest you to clear the autocomplete cache in your outlook and check the results .

Questions :

Is this issue is happening for all the users or it is coming for you only ?

What is the last change that you have done in your exchange servers ?

Hi ,

Below mentioned error message will come in the following situations .

Error Message : 550 5.1.1 RESOLVER.ADR.RecipNotFound; not found

1.you have added the smtp domain name "externalcompany.gov.uk" as authoritative domain in exchange and by not having the mail enabled contacts or mailbox for the users who belongs to that smtp domain suffix i.e (externalcompany.gov.uk") .

2.In few cases autocomplete cache in outlook will create such kind of issues.So for anyone of the affected user please flush the autocomplete cache in outlook and check the results .

By analyzing the error message i came to know that your exchange server 2013 is looking for the recipient (user1.thomas@externalcompany.gov.uk) in exchange and it not available because of that it is giving the bounce back error message to the sender.

Note : On your post you have mentioned that the bounce error is coming for you .So i would suggest you to clear the autocomplete cache in your outlook and check the results .

Questions :

Is this issue is happening for all the users or it is coming for you only ?

What is the last change that you have done in your exchange servers ?

The NDR clearly shows that the recipient address is rejected by remote server, i.e. next hop of the NDR generating server. Although the NDR is generated by your own Exchange server, the error code 550 5.5.1 comes from the remote server.

Are you 100% sure about this?

We route from exchange to a 3rd party mail filtering server (called websense). The bounced email is not even reaching here.

I know this because when I send an email to two email addresses (one of which I know works, one doesn't) all I see in websense logs is the one that works.

There is no 100% in my world. I'm 98% sure though. Of course this based on the NDR you posted.

The NDR is generated by ourexchange2013.mydomain.gov.uk because it received the error code from its next hop.

Hi ,

Thanks for your reply.

I mean to think you about the last major change that you have done in your exchange server and that could help most of the exchange admins to find out the RCA for the major issues.

Hi ,

Thanks for your reply.

I mean to think you about the last major change that you have done in your exchange server and that could help most of the exchange admins to find out the RCA for the major issues.

There is no 100% in my world. I'm 98% sure though. Of course this based on the NDR you posted.

The NDR is generated by ourexchange2013.mydomain.gov.uk because it received the error code from its next hop.

Thanks for the help. BUT, as per my other post, looks like the NDR was coming from our local exchange after all and not the next hop...

I did say NDR was generated by your own Exchange server, did I?

What happened is that when your Exchange server tried to send email to next hop, the next hop returns error 550 5.5.1 after the rcpt to command. Thus your Exchange cannot continue sending email and generate NDR.

If you enable protocol log on the send connector, you'll see all these details.