Article ID: 2807779 - View products that this article applies to.
When you send email messages to an internal user in Microsoft Office 365 dedicated, you receive an IMCEAEX non-delivery report (NDR) because of a bad LegacyExchangeDN reference. The IMCEAEX NDR indicates that the user no longer exists in the environment.
This issue occurs because the value for the LegacyExchangeDN attribute changed. The auto-complete cache in Microsoft Outlook and in Microsoft Outlook Web App (OWA) uses the value of the LegacyExchangeDN attribute to route email messages internally. If the value changes, the delivery of email messages may fail with a 5.1.1 NDR. For example, the recipient address in the NDR resembles the following:
To resolve this issue, use one of the following methods, as appropriate for your situation.
Method 1: Clear the auto-complete cache fileFor more information about how to clear the auto-complete cache file, click the following article number to view the article in the Microsoft Knowledge Base:
2005644Note The procedure that's described here has to be performed by each user individually.
(http://support.microsoft.com/kb/2005644/EN-US)The Outlook auto-complete file contains obsolete or invalid entries
Method 2: Create an X500 proxy address for the old LegacyExchangeDN attribute for the userTo create an X500 proxy address for the old LegacyExchangeDN attribute for the user, make the following changes based on the recipient address in the NDR:
X500:/O=MMS/OU=EXCHANGE ADMINISTRATIVE GROUP (FYDIBOHF23SPDLT)/CN=RECIPIENTS/CN=User-addd-4b03-95f5-b9c9a421957358dNote The most common items will be replaced. However, there may be other symbols in the LegacyExchangeDN attribute that will also be changed from the way that they appear in the NDR. Generally, any character pattern of "+##" must be replaced with the corresponding ASCII symbol.
If you are unfamiliar with the ASCII code in question, see ASCII Character Codes Chart 1