I have synced all leads from CRM to Zoho Marketing Automation. The name of the mailing list which contains all the leads is "All Leads"

Now I have created a mailing list named "Created in month of May". This mailing list should contain all the leads which were created in the month of May in CRM. Hence, I would first create a custom view in CRM and would sync to the list

But this list contains the leads which are already there in the "All Leads" Mailing list. Therefore I would like to know what would happen to the existing leads in this case

1. Will the leads be duplicated?

or

2. The leads will not be duplicated but will be synced in both the lists?