This email address could be in use by another user account.  If you know the account that is currently linked with the email forwarding address preform the following actions.
  1. Log in to Blackbaud Netcommunity
  2. Click on Users and security > users 
  3. Search for the user account that is currently tied with the email account you wish to forward to
  4. Remove the email address from the Incoming email address field 
  5. Ensure the enabled check box is not checked
  6. Click Save
  7. Edit the new user you wish to associate with this email forwarding address 
  8. Click Email forward
  9. Enter the email address to forward in the incoming email field
  10. Enter the email address to forward to in the Forwarding address
  11. Click Save

If you can not locate the user account that is currently tied with this email forwarding address please reach out to Customer Support