Short answer. It can be, but only if personal service was genuinely attempted first. Substituted service is allowed only after at least three attempts on two different dates fail for justifiable causes, and even then the copies must go to someone at least eighteen and of sufficient discretion residing at your residence.
What the law says
If, for justifiable causes, the defendant cannot be served personally after at least three attempts on two different dates, service may be effected: (a) By leaving copies of the summons at the defendant's residence to a person at least eighteen years of age and of sufficient discretion residing therein
Rule 14, Section 6 — Substituted service. Read the full provision →
Substituted service is a fallback, not a first option
The rule only allows this method if, for justifiable causes, the defendant cannot be served personally after at least three attempts on two different dates. Personal service on the defendant is the default; substituted service is available only once that has genuinely been tried and has genuinely failed, not simply because it seemed more convenient to hand the papers to whoever answered the door.
Who at the residence can be validly given the summons
Even when substituted service applies, copies of the summons can only be left with a person at least eighteen years of age and of sufficient discretion residing therein. A housemaid who is at least 18 and who actually resides at the home, with enough maturity to understand and pass along what she has received, can fit this description — but a minor, a casual visitor, or someone who does not actually live there would not.
Other valid ways to complete substituted service
The rule offers alternatives beyond service at the residence: leaving copies at the defendant's office or regular place of business with some competent person in charge, with an officer of a homeowners' association or condominium corporation or its chief security officer if entry is refused, or by electronic mail if the court allows it. Which method was actually used, and whether its specific conditions were met, matters just as much as whether service was attempted at all.
Why the details matter if you are contesting service
Because substituted service is an exception to the preferred method of personal service, its requirements are meant to be followed closely: the failed attempts, the two different dates, and the qualifications of whoever actually received the copies. A defendant who believes service on them was defective should look carefully at whether the sheriff's return actually shows these specific conditions were satisfied, rather than assuming any delivery to anyone at the address counts, since a defective substituted service can affect whether the court ever properly acquired jurisdiction over them.