Mont. Code Ann. § 32-1-1004

Service of process under this part may be made by delivering a copy of the papers to be served to the secretary of state personally or by filing a copy in the secretary of state's office, accompanied by one additional copy for each foreign trust company to be served. The secretary of state shall, no later than the business day following the date of service, mail to each served foreign trust company, by certified mail, a copy of papers that were served. The copies must be mailed to the address shown for each foreign trust company in the records of the office of the secretary of state.