Generate seperate dunning letters based due date of invoice

Summary:

If system sending final demand letter it must include the dues more than 60 days, If anything less than 60 days should go for Hard demand letter.But in now system considering all due invoices in dunning letter, the dunning leeter must include invoices bases its days late.The system should generate a separate letter for each invoice and mail it to the customer. Is it possible ?

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