Legal Question in Construction Law in California

Civil Code section 3097, subpart (f), sets forth how 20-day preliminary notices may be served. Sub-subpart (3) says "If service is made by first-class certified or registered mail, service is complete at the time of the deposit of that registered or certified mail." If you have proof of mailing and the returned envelope showing refusal, I'd say you have valid service on that party. Of course, 3097 probably requires you to serve more than one party, and it isn't completely clear from the wording of your question that you -- presumably a subcontractor or supplier -- served both the owner and the general, as probably necessary.

It does sound as if your service of the 20-day notice is contestible, even if not invalid. You have to serve the general AND the owner if you do not have a contract directly with the general, and fax service on the owner is not valid, though that defect may be waived if actually received and acknowledged. In any case, however, the thing to do is immediately serve another notice on both, and just use regular certified mail. Don't bother with the return receipt. It just mucks things up and isn't required. Worst case then is you lose stop notice and lien rights for work and materials used in the project more than twenty days before the new notice. A late notice doesn't mean all rights are waived.