Email to internal recipients fails with a 5.1.1 non-delivery report (NDR)

Brian Hadfield -

When you send email messages to an internal user on the Chinook Communications platform, you receive a 5.1.1 non-delivery report (NDR) because of a bad LegacyExchangeDN reference. The NDR may also indicate 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 (due to email migration or the re-creation of the user account or mailbox), 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, you will need to remove the user from the Outlook auto-complete cache file and then send a new e-mail selecting the user from the Global Address List.  Entries can be removed from your auto-complete file individually, or you can delete the entire file. If the file is deleted, Outlook creates a new file.

 NOTE: The auto-complete feature uses a file on your computer to store frequently used contacts. If you access your mailbox by using multiple computers, the auto-complete entries will vary from computer to computer. 

To remove an individual auto-complete entry

  1. Start a new email message in Outlook.
  2. Start typing the contact’s name until pre-populated contacts are suggested by Outlook.
  3. Use the Up and Down arrow keys to select the appropriate entry.
  4. Press the Delete key.
  5. Type the contact’s name or email address, and then press Ctrl+K.
  6. If the contact is an internal user, double-click the entry to make sure it resolves correctly by using the global address list.

If the contact is an external user, send that contact a test email message and confirm that it was received successfully.

To remove the entire auto-complete file

NOTE: These steps should only be used if there’s a problem with a large majority of entries in the your auto-complete file.  

  1. Close Outlook.
  2. Click Start, select Run, type %userprofile%, and then click Ok.
  3. Configure Windows Explorer to show hidden folders:
    a. In Vista or Windows 7, press and hold the Alt key to display the menus.
    b. On the Tools menu, click Folder Options.
    c. Click the View tab.
    d. Make sure that Show hidden files, folders and drives is selected.
    e. Make sure that Hide extensions for known file types is not selected.
    f. Click OK.
  4. In Vista or in Windows 7, open Appdata, Roaming, Microsoft, and then Outlook. In Windows XP, open Application Data, Microsoft, and then Outlook.
  5. Sort by the Date Modified column to show the most recent items at the top.
  6. Identify the most recently modified auto-complete file. The file name extension of an auto-complete file is ".nk2," and the file name has the name of the Outlook profile. If it is not clear which is the most current Outlook profile name, follow these steps:
              a. In Control Panel, click the Mail icon (Windows XP) or User Accounts - Mail (Windows Vista or Windows 7). 
              b. Click Show Profiles.
              c. The default profile will be listed under Always use this profile.
  7. Right-click the file, and then add .old to the end of the file name.
The next time that Outlook is started, a new auto-complete file will be generated.
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