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NDR - 550 - Mailbox unavailable

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I am a Microsoft Partner and administrator for an O365 account for a customer.  Emails sent to this customer's domain are bouncing with an NDR - 550 - mailbox unavailable.  Same results from several different servers.  DNS hosted by O365.  No changes have been made.  Suspect this is a forefront issue.  This issue has resulted in customer having no email service currently as they cannot recieve emails.

We have checked the portal.  Everything seems to be in order.

Need resolution quickly.


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  • I've got the same problem with my domain.

    Started yesterday. I still get a lot of emails but have had a number of people report to me that they are getting this bounce back message

  • Hello Pondo,

    Thank you for your post.

    Does this problem happen to all users in your domain, or just one user? Can the user who encountered this problem send emails out properly?

    I have checked the healthy status of Exchange Online and noticed that the service is always running. And I can send/receive emails properly with my test Office 365 mailbox. In our case here, to narrow down the issue, would you please send a test emails to/from your Office 365 account to reproduce the issue? And then, post back the full content of NDR message to allow us to understand the problem in more details.

    Thank you for your cooperation.

    Jack Sun

  • Sorry to hi-jack but I think my issue is the same.

    We are having multiple failures for different users.

    NDR Follows

    Delivery has failed to these recipients or groups:

    A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.

    The following organisation rejected your message:

    Diagnostic information for administrators:

    Generating server: #< #5.0.0 smtp;550 Requested action not taken: mailbox unavailable> #SMTP#

    Original message headers:

    Received: from ( by ( with Microsoft SMTP Server id; Mon, 30 Apr 2012 10:47:28 +0000

    Received: from mail94-am1 (localhost []) by

    (Postfix) with ESMTP id D221C460478 for

    <>; Mon, 30 Apr 2012 10:47:27

    +0000 (UTC)

    X-SpamScore: 0

    X-BigFish: PS0(zzc85dhzz1202hzzz2fh2a8h668h839hd25h)

    X-Forefront-Antispam-Report: CIP:;KIP:(null);UIP:(null);(null);;R:internal;EFV:INT

    Received-SPF: pass (mail94-am1: domain of designates as permitted sender) client-ip=;; ; ;

    Received: from mail94-am1 (localhost.localdomain []) by mail94-am1

    (MessageSwitch) id 1335782846174211_13993; Mon, 30 Apr 2012 10:47:26 +0000


    Received: from (unknown []) by (Postfix) with ESMTP id 25CCA340045 for

    <>; Mon, 30 Apr 2012 10:47:26 +0000 (UTC)

    Received: from ( by ( with Microsoft SMTP Server (TLS) id; Mon, 30 Apr 2012 10:47:22 +0000

    Received: from ([]) by ([]) with mapi id

    14.16.0143.004; Mon, 30 Apr 2012 10:47:16 +0000

    From: Darren Baines <>

    To: "" <>

    Subject: Test

    Thread-Topic: Test

    Thread-Index: Ac0mvpvYELl/ozSTTOyc1PLbQmjmIw==

    Disposition-Notification-To: Darren Baines


    Return-Receipt-To: <>

    Date: Mon, 30 Apr 2012 10:47:16 +0000

    Message-ID: <>

    Accept-Language: en-GB, en-US

    Content-Language: en-GB



    x-originating-ip: []

    Content-Type: multipart/alternative;


    MIME-Version: 1.0



    X-FOPE-CONNECTOR: Id%0$Dn%*$RO%0$TLS%0$FQDN%$TlsDn%


  • Same issue, started on Saturday.  I haven't heard anything from Microsoft on this.  Need resolution.

  • Are any of you still experiencing this problems? If so, does the NDR contain a line similar to this:

    The following organisation rejected your message:

    I haven't received any new indications of this since April 30th and I want to know if this is still happening before I escalate this to the engineers.



  • The problem seems to be resolved and only lasted th.  I did not have an NDR line like the one you posted.  The oddest part was that the bouncebacks were not consistent, they happened to different people at different times from different external servers.