Me. Rev. Stat. tit. 14, § 6208

An action on a mortgage deed may be brought against a person in possession of the mortgaged premises. The mortgagor or person claiming under him may, in all cases, be joined with him as a cotenant, whether he then has any interest or not in the premises, but he is not liable for costs when he has no such interest and makes his disclaimer thereto upon the records of the court. <div