By default, Manyreach only imports new prospects to the campaign and/or CRM. The unique identifier is an email address. This is implemented to prevent you from accidentally sending campaigns to prospects you already contacted.
If an email address already exists in the Manyreach CRM it won't be added to the campaign unless you select "Insert if already exists in main database and update it".
This will update the prospect's properties in the main CRM and import them to the campaign.
