Your question is a bit incomplete, but my guess is that you are referring to a small claims court lawsuit wherein you asked the clerk of the court to effectuate service of the Plaintiff's Claim via certified mail? If so, the actual defendant you are suing must sign the return receipt on the certified mail. Otherwise, the defendant can challenge the service and file a motion to vacate the default judgment.
Frank W. Chen has been licensed to practice law in California since 1988. The information presented here is general in nature and is not intended, nor should be construed, as legal advice for a particular case. This Avvo.com posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, please consult with your own attorney.