Hi Mike
There are two ways to do this. You can either :
(A) Set up a Message Rule to detect a failure on the Send Port and then trigger an appropriate process
or
(B) Set the Send Port to send synchronously (Tracking and Diagnostics tab) - in this case any error in sending will be reported to the Workflow synchronously and can be handled as an exception.
Thanks,
Ben.
Ben Jackson
SmartsIntegrator Technical Support