(a) (1) If, on affidavit of the plaintiff, it appears to the satisfaction of the court that the plaintiff has used reasonable diligence to ascertain the identity and residence of and to serve a summons on the persons named as unknown defendants and persons joined as testate or intestate successors of a person known or believed to be dead, the court shall order service by publication in accordance with Rule 2–122 of the Maryland Rules and the provisions of this subtitle. (2) The order shall direct that a copy of the summons, the complaint, and the order for publication be mailed immediately to the party if the party’s address is ascertained before expiration of the time prescribed for publication of the summons. (b) This section does not authorize service by publication on any person named as an unknown defendant who is in open and actual possession of the property.
Maryland Legal Code