This Error event indicates that outbound SMTP authentication on the specified Send connector failed with the specified destination smart host server. Typically, this error indicates an authentication problem on the Send connector, not on the target smart host server. This error is most likely caused when the Send connector is unable to obtain a Kerberos ticket for the target smart host server that is specified in the error message text.
When a Send connector is configured to route outbound messages to a smart host, the following authentication methods are available:
In the Exchange Management Console, you set the authentication methods for outbound connections to a smart host on the Configure Smart Host Authentication Settings tab after you click Change on the Network tab of the Send connector properties page.
In the Exchange Management Shell, you set the authentication methods for outbound connections to a smart host by using the SmartHostAuthMechanism parameter on the Set-SendConnector cmdlet.