Skip email based on response message.

Use hook ...remote_success to modify/use the $form variable dependent on the original plugin (i.e. CF7 form object would be manipulated differently than GF form array).

You’ll see in the source code where this happens, and note that you’ll have access to that $refs variable (passed to the hook as the second argument $callback_results) so you can set a flag to decide whether to skip: https://github.com/zaus/forms-3rdparty-integration/blob/737892367f26f5895bfade7f944c28ed2e5ec42d/forms-3rdparty-integration.php#L710