Thank you for reaching out to us, we are here to help.
Your first question is a bit hard to understand, but I think it is best to read our onboarding documentation about the live and test options that our plugin provides here. You switch the modes by simply clicking on the checkbox and when you are testing, you can use sandbox accounts that you can create on the PayPal Developers site.
Our plugin does not actually send emails, this is done by WooCommerce and the PayPal server. I am not sure what situation you are asking about and since it is not controlled by our plugin, there is not much I can tell/advise you on this in any case. This is all handled by WooCommerce, so it might be best to talk with them. If you want to change the emails that are sent by PayPal, you should check in the settings of your PayPal Merchant account.
I am not sure if I understood your questions correctly, so please send me another message if you did not get your questions answered. If you want to share screenshot, logs or other details with us, but don’t want to do it on a public forum, you can always open a private engagement with us here.