Send E-Mail Failure

first thing is to make sure you have configure your send email node with proper configuration and second thing is to have an exception configured on that node based on certain condition.

Why you want to end the process if there is an error? The process will still remain in active with errors state.

Anyway, I think you cannot create an exception flow as there is no flag returned for success or failure of this smart service and hence it is not possible to create an exception rule and timer also won't work on the node as the node is not active.

You can terminate the process by adding an another flow which will wait for Send EMail node to execute and if it fails and the waiting time reaches the threshold limit set by us in timer event then the process will terminate.