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Bounce-back error “550 Requested action not taken: mailbox unavailable”

Home Forums Messaging Software Exchange 2007 / 2010 / 2013 Bounce-back error “550 Requested action not taken: mailbox unavailable”

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    Occasionally when mailing random people on our exchange server 2010, the sender receives a bounce back that says: The e-mail account does not exist at the organization this message was sent to. Check the e-mail address, or contact the recipient directly to find out the correct address. < #5.1.1 SMTP; 550 Requested action not taken: mailbox unavailable>

    This is a full detailed message:

    Delivery to the following recipient failed permanently:

    Recipient’s email

    Technical details of permanent failure:
    Google tried to deliver your message, but it was rejected by the server for the recipient domain (Domain name) by (mail server Name). [Mail server IP].

    The error that the other server returned was:
    550 Requested action not taken: mailbox unavailable

    Original message

    DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20120113;
    X-Received: by with SMTP id gb8mr5871250igd.44.1423856384558;
    Fri, 13 Feb 2015 11:39:44 -0800 (PST)
    Received: from [] ([])
    by with ESMTPSA id j5sm4975644iod.31.2015.
    (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128);
    Fri, 13 Feb 2015 11:39:43 -0800 (PST)
    Subject: Test 2:38
    From: Sender
    Content-Type: text/plain;
    X-Mailer: iPhone Mail (11B511)
    Message-Id: <[email protected]>
    Date: Fri, 13 Feb 2015 14:38:25 -0500
    To: Recipient
    Content-Transfer-Encoding: 7bit
    Mime-Version: 1.0 (1.0)

    Now the email is sent to the correct email address and usually after several minutes if the sender attempts to send the email again, it goes through just fine. At the time that this occurs, there are no errors in the event viewer and no logs in the exchange server.
    I also searched the firewall and i cant see any logs for that email message…
    From all that I read on this error, everyone reports that it means the mailbox doesn’t exist. Has anybody every encountered an issue like this?

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