I have a data list that consists of new leads and likely existing contacts. (607 people)

I want to import the leads into the leads module, but how do I exclude contacts I will not know and vice versa? How do I import the list into the contacts module but not end up importing the leads that do not belong there?

I have attempted this, and it duplicates, as the modules do not talk to each other.

I  have spent several hours today with Zoho, and they have no resolve.

Does anyone have a solution?