Hi @guptaanjali538 ,

Once you create your signup form and it’s routing to a mailing list, you can apply a behavior setting to the signup form so that it doesn’t display for people on a list. This only works if those people have been cookied in your account by signing up through the Klaviyo form or clicking through a Klaviyo email to your website. 

While we are unable to notify a person if they attempt to signup through a signup form to a list that they have already subscribed to, if that does happen you there are few other things to consider:

1. You can always update the success message of the signup form letting them know that the deal being offered only applies to new subscribers.
2. If you have a flow triggered off of someone subscribing to a list, if that user already exists on the list, they will not trigger that flow. It only triggers for new subscribers.

Have a nice weekend!

Julie