We migrated our Exchange server to anySiteHosting.com’s hosted Exchange service, and now when send new emails we get NDR 5.1.1 errors even after deleting the NK2 file or cached email addresses.
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:
Since the process of deleting the object from the .NK2 cache did not work then we would want to follow the instructions below to resolve the issue.
Create an X500 proxy address for the old LegacyExchangeDN attribute for the user
To 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:
Replace any underscore character (_) with a slash character (/).
Replace “+20” with a blank space.
Replace “+28” with an opening parenthesis character.
Replace “+29” with a closing parenthesis character.
Delete the “IMCEAEX-” string.
Delete the “@mgd.domain.com” string.
Add “X500:” at the beginning.
After you make these changes, the proxy address for the example in the above section.
X500:/O=MMS/OU=EXCHANGE ADMINISTRATIVE GROUP (FYDIBOHF23SPDLT)/CN=RECIPIENTS/CN=User-addd-4b03-95f5-b9c9a421957358d
Note 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.
APPLIES TO / KEY WORDS