I'm currently busy personalising my newsletter form and I'm succeeding in doing everything I wanted to do (design, displaying the success message, etc.) but there is something I'm not able to do and I found no documentation about it.
I would like to display a message if someone who is already in the database fills the form.
Something like "Thanks for subscribing but you're already part of the database."
FYI my subscription form is linked to Mailchimp.
Thanks a lot for your help.