“550 5.1.1 RESOLVER.ADR.ExRecipNotFound” NDR error message when you send email messages by using Outlook in Office 365



When you send email messages by using Microsoft Outlook in Office 365, you may experience one or both of the following issues:

Symptom 1: You receive non-delivery reports (NDRs)

Email messages or meeting invitations are not delivered successfully. For example, you receive an NDR that resembles the following:Generating server: <server name>.local

IMCEAEX-_O=CONTOSO_ou=first+20administrative+20group_cn=Recipients_cn=<username>@<server name>.local

#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##

Symptom 2: The AutoComplete feature in Outlook does not work as expected

When you create a new email message and then type a name in the To line, the user’s name is auto-populated. However, when you double-click the name, you experience one of the following issues:

  • The dialog box information is not displayed correctly.
  • Information is missing from the dialog box.


These issues may occur if one of the following conditions is true:

  • You reply to messages that were migrated from personal folders (.pst) files or were migrated by using a third-party migration tool.
  • The Outlook nickname cache (AutoComplete) contains a bad entry.
  • The OfflineAddressBook is not updated or cannot be downloaded.


To resolve these issues, follow these steps:

  1. Reset the nickname and the autocomplete caches in Outlook. For more information about how to do this, click the following article number to view the article in the Microsoft Knowledge Base:287623 How to reset the nickname and the automatic completion caches in Outlook
  2. If you reply to a migrated message, type the whole email address of the recipient again. If the Autocomplete feature tries to input the recipient name or address for you, click the “X” to delete the entry, and then manually type the whole email address again.

  3. Make sure that the Offline Address Book is operating correctly. For more information about how to troubleshoot the Offline Address Book, click the following article number to view the article in the Microsoft Knowledge Base:2429946 How to troubleshoot the Outlook Offline Address Book in an Office 365 environment

Source: https://support.microsoft.com/en-gb/help/2784785/550-5-1-1-resolver-adr-exrecipnotfound-ndr-error-message-when-you-send

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Phuong Nguyen
Hi, Nguyen Van Phuong is the owner of the website viettechgroup.vn. I 've been working in the IT sector since 2008. With nearly 12 years experience in the fields of design development, Governance, operating system enterprise network infrastructure.. I'm now a senior Infrastructure Administrator for the Enterprise network. Achivements: IT Project management IT management System and Network IT Security and data protection. Plan and bugged for Infrastructure and Security Deployment system Server (HP, IBM, Lenovo, Dell..), Network (Cisco, Juniper, Enterasys,..), PABX system, Firewall (Cisco ASA 5525-x, Juniper SSG520,..) Network system administration and maintenance: +Management all network configure IT system: AD, DNS, DHCP, Cores switch, Access switch, Router, Firewall, etc. Design & implement IT system, project management and manage IT operation, I also have extensive experience of ERP System base SQL , HRM, etc. Vendor/external system integrator management: support other department in terms of technical specifications for cost optimize, business process efficiency, procurement spend compliance. Virtualization System Deployment on Microsoft Windows Server 2016 (Hyper-V) and VMware ( Vmware vSphere 5.5, 6.5,6.7 vCenter) Backup and restore management on Symantec backup products (Veritas Backup 16, 20, 20.1, 20.2 ), Veeam Backup & Replication 9.0, 9.5U1, 9.5U2 U3, U4


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