Check if email exists

Hi, Thanks so much for this plugin it works awesomely and very easy to use!

One thing I would like to have (or know if exists already): if a customer fills in the form and the email already exists in Sendy, I would like the option to return a message saying “this email already exists” (or better a custom message).

Currently it just overwrites all other fields (or makes blank if something is not filled out) which is useful in some cases. So best would be to have two options when email exists: A) don’t update to Sendy and throw custom message B) update/overwrite all fields.

Thank you!