Important: Double user registration

Hello, I would like a user when I subscribe to a list for the second time (therefore with the same e-mail) I get an email or a notice.

Right now I have 2 lists set up as follows:

• form1 on my website (written in html with Active Campaign API) → list 1 registration → autoresponder with confirmation of registration

• form2 on my website (integrated and built into Active Campaign, from the modules section) → autoresponder with confirmation of registration

When a user signs up a second time, obviously he is not added to the lists if he has the same e-mail, but I need to receive a notice of this second sign up. how can I activate it in both lists?

Thanks in advance