With dunning letter feature turned on, a new tab appears in AR preferences where you can identify Dunning Level 1, 2, 3, and at how many days each letter is sent. Customer Mailing Settings tab in AR Customer Profiles screen lets us specify Dunning Letter email recipients. The letter itself is an Acumatica report #AR661000 that can be modified/copied using the Acumatica report writer. It has been many years since I worked with Dunning Letters, but *I think* we had if statements built into report AR661000 that caused a particular body to print on the letter where Dunning Level = 1, a somewhat harsher letter body where dunning Level = 2, and so on. You can ‘opt out’ customer classes or individual customers, and also could have entirely different letters for different customers or classes using different report numbers connected to the Mailings tab of the customer screen.