Me. Rev. Stat. tit. 14, § 6107

When it is alleged under oath in the complaint that the mortgagees or persons claiming under them are unknown or that their names are unknown, they may be described generally as claiming by, through or under some person or persons named in the complaint. Service shall be made as in other actions on all known defendants residing either in the State or outside the State, and notice by publication to defendants whose identity or whereabouts are unknown shall be given as in other actions where publication is required. <div