If it is actually resending the message it should also log something about success on retry x where x is the number of times it retried to send the message.
You can also disable the retry mechanism by adding this to user.config:
<add key="TimesToRetryOnSmtpError" value="0" />
I've just now updated the code so it will log the error detail on smtp errors in the next release. Nothing will show up in Event Viewer because that only shows unhandled exceptions, this exception is a handled exception ie its in a try catch and the catch has retry logic.
Hope that helps,
Joe