We have license for 500k contacts. Currently we have 400K unsubsribers in our database. If we import 400K unsubscribers in Marketo, then it will consume for 400K contacts and we will be able to upload only 100K subscribed contacts. So we don't want to import unsubscribed contacts into Marketo. We want that when user imports contact list in Marketo, it should validate each contact/lead against our unsubscribe database and then add the contact in Marketo (if contact does not exist in unsubscribe database) . Is there any way to customize the Upload List Feature in Marketo ? Can we write/plugin some kind of component in Marketo to achieve this?
If the customization is not possible, is there any other alternate to this. Please suggest.