Tenants broke their lease and have refused notices to pay up. I cannot serve the court papers because they live in a PO Box in another town. Can I turn them into a collection agency without sewing them in small claims court?
A collection agency is going to want to see a legal judgement or legal proof that you are entitled to the debt.
You can send Certified Mail to a P.O. Box in the United States. USPS Certified Mail letters are addressed and delivered to the PO Box with no changes in mailers process. In other words you just address the letter using the PO Box instead of the street delivery address. When the USPS letter carrier delivers the letter the process that documents when the letter was received at the delivery address is a little bit different. A delivery notification card is placed inside the PO Box instructing the recipient they have a Certified Mail waiting for pick up from the Post Office window clerk. Because USPS requires someone to sign for each Certified Mail letter the delivery notification card must be presented to the window clerk at the USPS Post Office. Then the recipient is presented the delivery confirmation Signature card and the date and time of the delivery confirmation are electronically captured and recorded by USPS. This is how the United States Postal Service handles delivery when you address a certified mail label or form with a PO Box.
You can do a little research on the internet and see if a new address is available for them through search sites such as whitepages.com or 411.com.
You can also serve the court papers at their places of employment.