Time passes and receivable management methods evolve.If the postmail letter was a much used dunning action in the past, it is now almost obsolete except for sending the formal notice.
Times are also shortening naturally because of the demand for quicker results and the improvement of communication and payment tools between the seller and the buyer.
The tutorials about collection of accounts receivables have therefore evolved accordingly, you will find them here:
These tutorials are very oriented collection management in B to B (company that sells to another company).