In California, substitute service can occur once a reasonable effort to perform personal service has been attempted and documented. In practice, this means that 3 attempts must be made before substitute service can be performed. When sub-serving, we must have confirmation that the defendant lives at the address, and the recipient must be 18 or older and live at the address with the defendant.
You can even substitute serve on the third provided you enter an attempt in ABC Mobile before the service. Here's what that looks like:
You have made two attempts at a residence and on the third trip there, someone answers the door. You ask for the defendant by their full name and the person confirms that the defendant lives there with them, but they are not available at the time. You may now hand the documents to that person. Afterwards, go into ABC Mobile and log an attempt that explains how you attempted to personally serve the defendant. This would be the third activity on that order, visible in the history tab of ABC Mobile. Afterwards, you are free to enter the service details.
It won't always be the case that someone opens the door after three attempts. In this case continue to try and meet Due Diligence.
If the service location is determined to be a usual place of mailing for the subject, substitute service may be executed. In other words, if you speak to a resident who confirms that the servee receives all of their mail at the location but it is not their usual place of residence, you may serve.
When considering substitute service at a usual place of mailing, consider the likelihood that the documents will in fact be received by the subject. If you do not reasonably believe the sub service will result in the reception of the documents by the subject, most likely neither will the court.
It is better to mark an address as a bad address rather than execute a sub service to a questionable place of mailing.
Substitute service is allowed on the first attempt at private mailbox facilities. Private mailbox facilities include UPS and Fed-Ex facilities, as well as smaller privately owned businesses. Process servers must verify the subject is a box-holder at the location.
Service at United States Postal Service locations is strictly disallowed. Under no circumstances does a USPS qualify as a private mailbox facility.