Form POS-030, Proof of Service by First-Class Mail - Civil is a proof of service form for documents served to one or more parties to a civil action.
The State of California allows serving papers by sending them to the party to the proceedings via first-class mail that produces a return receipt. This is a cheap and easy method to serve papers, and the service is accomplished even if a letter is rejected by the addressee. A court has no way of knowing whether or not documents have been successfully sent by first-class mail unless you tell them, and notification is possible by filing a POS-030 Form.
This form was released by the California Superior Court. The latest version of the form was issued on January 1, 2005, with all previous editions obsolete. A POS-030 fillable form is available for download below.