[FIXED] Exchange Error: 550 5.1.1 RESOLVER.ADR.ExRecipNotFound

When you send an email using Outlook, you might receive a Non-Delivery Report (NDR) or encounter other issues. This would mean that there is a problem delivering the email to one or many recipients.

The error you receive would be like the below:

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 ##

This could occur when sending out an email, calendar request, or a notification email from the system. You would also get the similar error when you create a new message and start typing in the To, Cc, or Bcc field and Outlook autocompletes the recipient’s email address.

When you double-click on the name from the autocomplete, you will encounter the following issues:

• Missing information in the pop-up window with more details.
• The pop-up window is not displayed correctly in your view.

Reasons for the 550 5.1.1 RESOLVER.ADR.ExRecipNotFound Error

There could be several reasons why this error occurs. Let’s look at some common reasons:

• You had an exported PST which was attached to your Outlook or may have migrated emails from another mailbox using a migration tool.
• The Outlook cache which is known as auto complete, would be either corrupted or contains a bad entry which is affecting the delivery of emails.
• The Offline Address Book (OAB) which is synchronized with your Exchange Server is not updated, corrupted, or not synchronizing.

Solutions to Fix 550 5.1.1 RESOLVER.ADR.ExRecipNotFound Error

There is no exact solution to resolve this error. Here are some possible fixes you can try to resolve the issue.

Clear the Auto Complete of the Affected User

You can search for the affected recipient in the To, Cc, or Bcc field. When it appears, click on the X on the right-hand side. This will delete the cached contact.

After this, you can try to re-send the email to the user.

Clear the Outlook Cache and Autocomplete

If the above solution does not work, you can clear the Outlook cache and autocomplete. This would confirm the local cache is re-built. Follow these steps:

• Open Outlook and click on File.

• Click on Options.

• Click on Mail on the Outlook Options window.

• Scroll down until you find the section called Send messages.
• Click on Empty Auto-Complete List.

• After the cache is cleared, close Outlook and open it again. Then, check if the problem has been resolved.

Move Mailbox to Another Database

There could be an issue with your Exchange Server where the Offline Address Book (OAB) is not updating the X.500 distinguished name information of the original recipient. This usually happens when you import data via PST files.

To resolve the issue, you can move the mailbox to another Exchange Server mailbox database if the issue is related to only one user.

Force Update Address Book

If the address book is not updating of all the users, then you can run the following command to try to force the update.

Update-OfflineAddressBook -Identity "Default Offline address Book"

Before running the above command, you need to make sure that Microsoft Exchange Mailbox Assistant and Background Intelligent Transfer Service are running.

Alternate Solution

An alternate solution would be to re-install the Exchange Server. In this case, to avoid any data loss, you can use the best companion application for any Exchange Server – Stellar Converter for EDB. The application allows you to open multiple Exchange Server mailbox database (EDB) files from any version of Exchange Server. With this, you can browse all the mailboxes and public folders.

You will be able to view the emails and data in full HTML view. You can granularly export to PST and other formats, such as EML, MSG, PDF, and HTML. You can export directly to a live Exchange Server database. The application is not limited to user mailboxes only as you can also export shared mailboxes, user archives, disabled mailboxes, and public folders with no limit on size of the item or database.

All this without having an Exchange Server installed. The application can be installed on a Windows 10 or Server operating system. You can also use the application to migrate to Office 365 with ease.