How may an individual serve a summons within a judicial district of the United States?

The correct choice highlights that an individual may serve a summons according to state law or through personal delivery, which is in line with procedural rules governing service of process in various jurisdictions. Each state has its own specific laws dictating how service of process must be conducted, including acceptable methods such as personal delivery, mail, or sometimes even publication in certain circumstances.

Personal delivery ensures that the defendant receives the summons directly, promoting fairness by providing clear notice of the legal action. Additionally, many jurisdictions allow service by mail, requiring certain conditions to be met, such as a return receipt.

The other options do not encompass the necessary legal framework adequately. Serving by postal service only limits the methods available, while relying solely on electronic communication is not universally acceptable, as not all jurisdictions recognize such methods for serving legal documents. Therefore, the provision for adherence to state law and the allowance for personal delivery captures the broad range of acceptable and legally recognized methods of service.