You get the error message that your Outlook, using your Gmail address, will no longer send messages. You can receive them, but not send and they are stuck in the Outbox.
To resolve, open Outlook, click on File, Account Settings, Account Settings again, then select the affected account. Click on the menu option Repair. Then click the Advanced link and check the box to let you repair manually and then click Next. Then, expand outgoing mail to see the options. Check the box to require secure authentication, (SPA). Click Next and then Done. Close the Account settings window.