see the "Debugging eCart transaction failed issues" tutorial on the eCart support page:
When adding the local checkout response binding group, make sure to select "Authorize Express Checkout" as the gateway. You should also add a second one for "Process Express Checkout"
add the Long error message binding from both of those binding groups to the failure page to get info on why the transaction is failing.
If the email is not sending, you should double checkout the smtp server address and the From address being used in the Universal Email server behavior.
double check with your host if you are not sure what to use.
If you are convinced these are set correctly, ask you host to look into the smtp server error logs to see why the smtp server is not relaying the email message.