550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found’

NDR error message when you send email messages using Outlook


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.


1. Disabling Cache exchange mode

  • On the Tools menu, clickAccount Settings.
  • On the E-mail tab, click the Exchange account, and then click Change.
  • Under Microsoft Exchange server, clear the Use Cached Exchange Mode check box.
  • Exit and restart Office Outlook

2. Re-adding autocomplete

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.

A screen shot of the To line, showing the auto-populated address and the

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