How to make a black list in this case.

Please tell me. How to make a black list in this case. To receive only unique email values. So that the same value is not sent several times @client.on(events.NewMessage()) async def normal_handler(event): text = event.message.to_dict()['message'] if re.search(r'[^\s]+@[^\s]+', text): m = re.search(r'[^\s]+@[^\s]+', text) await client.send_message('@LOGIN', m.group(0)) print(m.group(0))