Foundry Form – how to turn off success / failure message

I’m using the form from Elixir Graphics Foundry to allow web visitors to send messages. Clicking submit prompts a success / failure message. But increasingly my form is being spammed. The form sends a message to the spammer and of course it bounces off their email address and I get a mail delivery failure message and these clog up my inbox. I don’t really need them. So how do I stop the form sending a success / failure message in the first place?

put a captcha on the form hopefully it can stop some of it