Error: "We Won't be Able to Deliver This Message to XXX, Because the Email Address is Invalid".

Error Message

We won't be able to deliver this message to XXX, because the email address is no longer valid.

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Description

These errors can occur because your Outlook application saves—or "caches"—information for email addresses that you have sent messages to in the past. After a mailbox move, this cached contact information may not update in time to point to the new Microsoft 365 email system, and like an out-of-date phone book, is instead still referencing the information for where the contact used to be in the old email system.

Resolution

To resolve the error, there are two options:

  1. Remove just the one contact you're noticing the issues with. (This is the recommended option.)

  2. Clear the entire cache for all contacts.

Remove a Single Cached Contact from Outlook (Recommended)

  1. Open your Outlook application
  2. Click New Email

        3. Start typing the name or email address for the contact you'd like to send to

        4. You will notice a pop-up below the "To" field that contains the contact's information

        5. To the right of the contact's information, there is a small X - Click this X to remove the contact
           

        6. The contact is now removed from the local cache

        7. Start retyping the contact's email address, but don't click anything until the complete email address is entered

        8. Once the complete email address is entered click the Check Names button in Outlook
             

       9. After clicking Check Names, the email address and contact will now be re-saved and cached in your Outlook application

     10. You are now able to resend your email message to that contact

Remove All Cached Contacts from Outlook

  1. If you would like to preemptively clear all cached addresses from Outlook, you can do so with the following steps.

  2. Open your Outlook application

  3. Click File
    Outlook application with the File button highlighted
  4. Click Options
    Outlook application file menu with Options button highlighted.
  5. On the left-hand navigation menu, click Mail
    Outlook application Options menu with the Mail menu item highlighted.
  6. Scroll-down 2/3 of the way to the bottom on the Mail options screen to the heading "Send Messages"
  7. Under the Send Messages heading, click the button that says "Empty Auto-Complete List"
    Outlook application Mail Options screen with the Empty Auto-Complete List highlighted.
  8. Click Yes to confirm emptying the Auto-Complete List
    Outlook application Empty-AutoComplete List confirmation dialogue box with the Yes option highlighted.
  9. Close Outlook
  10. Re-open Outlook
  11. The next time you compose an email, after entering in an email in "To" field, click the Check Names button in Outlook
    New Outlook email message showing an email address in the To field and highlighting the Check Names button on the ribbon.
Additional Information

For the most efficient support experience, please submit a ticket using the "Get Help" button, or call 531-622-2900.