Delivery Has Failed to a Known Good Address | ExchangeDefender [ Skip to content ](#main) [ ![ExchangeDefender](/assets/images/xd_logo_blue.png) ](/) Email Security ![Platform Overview](/assets/images/m-xd-pro.png)### ExchangeDefender PRO Enterprise-grade email security made simple for every business. 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The answer is no! It is not because we do not want to answer it, but because it is impossible. There is a very easy way to spot a rejection at client side (meaning the mail client). The address that it is trying to reach is NOT the address you are sending to but something along the lines of IMCEAEX… #### Here’s What the Rejection Will Look Like: > #### **Delivery has failed to these recipients or groups:** > > ['John Doe'](mailto:IMCEAEX-E@exchange.exchangedefender.com)The e-mail address you entered couldn't be found. Please check the recipient's e-mail address and try to resend the message. If the problem continues, please contact your helpdesk. > > **Diagnostic information for administrators:** > > Generating server: XDHUB1.exchange.exchangedefender.com > > \#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ## > > Original message headers: > > Received: from XDMBOX2.exchange.exchangedefender.com (\[fe80::a8e2:9126:dd6e:8bf8\]) by XDHUB1.exchange.exchangedefender.com (\[::1\]) with mapi id 14.02.0247.003; Wed, 25 Jul 2012 13:59:14 -0400 Content-Type: application/ms-tnef; name="winmail.dat" Content-Transfer-Encoding: binary From: Pete Doe <> To: ‘John Doe' <> Subject: Test Thread-Topic: Test Thread-Index: Ac1pDVsDxEcqf72fRmijT1S+CcvrRA== Date: Wed, 25 Jul 2012 13:59:25 -0400 Message-ID: <> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: <> MIME-Version: 1.0 X-Originating-IP: \[123.123.123.123\] #### Here’s the Background on the Issue: Outlook maintains a nickname list that is used by both the automatic name checking feature and the automatic completion feature. The nickname list is generated automatically as you use Outlook. If the nickname cache is corrupted, Outlook may be unable to identify recipients, may offer incorrect recipients when automatically completing the email address, or may send the message to the wrong person. #### Here’s How You Fix It: ##### *Outlook 2010* > 1\. Open a new email message. > > 2\. Type the first few characters of the nickname cache entry that you want to remove from the cache. [![Fix It](http://www.exchangedefender.com/blog/media/Delivery_BFB6/Fix-It_thumb.jpg)](http://www.exchangedefender.com/blog/media/Delivery_BFB6/Fix-It.jpg) > > 3\. When the entry appears in the list of suggested names, move your mouse pointer over the name until it becomes highlighted, but do not click the name. > > 4\. When the “X” icon appears next to the highlighted name, click X to remove the name from the list. ##### *Outlook 2007 or Outlook 2003* > 1\. Open a new email message. > > 2\. Type the first few characters of the nickname cache entry that you want to remove from the cache. > > 3\. When the entry appears in the list of suggested names, use the UP and DOWN arrow keys on your keyboard to select the entry, and then press DELETE on your keyboard. [Outlook Knowledge Base Article](http://support.microsoft.com/kb/287623)["Fix it" Download](http://go.microsoft.com/?linkid=9759542) Carlos Lascano VP Support Services, ExchangeDefender (877) 546-0316 x737 [ Previous post CloudShare Q&A July 26, 2012 ](https://www-preview.exchangedefender.com/blog/2012/07/cloudshare-qa) [ Next post ExchangeDefender NOC & Android App July 31, 2012 ](https://www-preview.exchangedefender.com/blog/2012/07/exchangedefender-noc-android-app) Related Posts ------------- [ 1 May ](https://www-preview.exchangedefender.com/blog/2026/05/exchangedefender-new-ui-is-live)### [ExchangeDefender New UI is Live](https://www-preview.exchangedefender.com/blog/2026/05/exchangedefender-new-ui-is-live) [Read more: ExchangeDefender New UI is Live](https://www-preview.exchangedefender.com/blog/2026/05/exchangedefender-new-ui-is-live) [ ![](https://storage.services.exchangedefender.network/exchangedefender-blog/blog/2025/12/christmas-1.jpg) 25 Dec ](https://www-preview.exchangedefender.com/blog/2025/12/merry-christmas)### [Merry Christmas](https://www-preview.exchangedefender.com/blog/2025/12/merry-christmas) [Read more: Merry Christmas](https://www-preview.exchangedefender.com/blog/2025/12/merry-christmas) [ ![](https://storage.services.exchangedefender.network/exchangedefender-blog/blog/2025/11/Website-Screenshots-2025-4.jpg) 4 Nov ](https://www-preview.exchangedefender.com/blog/2025/11/why-iot-devices-are-a-hidden-security-risk-for-your-business)### [Why IoT Devices Are a Hidden Security Risk for Your Business](https://www-preview.exchangedefender.com/blog/2025/11/why-iot-devices-are-a-hidden-security-risk-for-your-business) [Read more: Why IoT Devices Are a Hidden Security Risk for Your Business](https://www-preview.exchangedefender.com/blog/2025/11/why-iot-devices-are-a-hidden-security-risk-for-your-business) Search the blog Search Recent Posts ------------ - 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