This message occurs when the recipient has changed their email configuration and Outlook thinks there should be one type of server (like an exchange server) on the other end and there is not. The problem occurs because Outlook saves the type of email address it is interacting with in the contact record. To fix, do the following…
1. Open New Email and add the recipient's name in the To field.
2. Double-click the email address.
3. Click View More Options to interact with this person and select Outlook properties:
4. In the contact card, double-click the email address.
5. Click View More Options to interact with this person and select Outlook properties:
6. Change the Email type to SMTP:
7. Send this new message.
Note: If you don't send a message after making this change it will revert back once the mail message is closed.