43 C.F.R. § 3712.2-6
The last paragraph of section 5(a) of the Act provides with respect to service of the notice by personal delivery or by registered mail, as follows:
Within fifteen days after the date of first publication of such notice, the department or agency requesting such publication (1) shall cause a copy of such notice to be personally delivered to or to be mailed by registered mail addressed to each person in possession or engaged in the working of the land whose name and address is shown by an affidavit filed as aforesaid, and to each person who may have filed, as to any lands described in said notice, a request for notices, as provided in subsection (d) of this section 5, and shall cause a copy of such notice to be mailed by registered mail to each person whose name and address is set forth in the title or abstract company's or title abstractor's or attorney's certificate filed as aforesaid, as having an interest in the lands described in said notice under any unpatented mining claim heretofore located, such notice to be directed to such person's address as set forth in such certificate; and (2) shall file in the office where said request for publication was filed an affidavit showing that copies have been so delivered or mailed.
43 C.F.R. § 3712.2-6