C.R.S. § 13-40-112: Service.

(1) A summons may be served by personal service as in any civil action. A copy of the complaint must be served with the summons. If a defendant provides the plaintiff with written or actual notice that the defendant is a victim-survivor of unlawful sexual behavior, stalking, domestic violence, or domestic abuse, the plaintiff shall only perfect service through personal service to the defendant who provided the written or actual notice.

(2) Except as provided in subsection (1) of this section, if personal service cannot be made upon the defendant by a person qualified under the Colorado rules of civil procedure to serve process, after having made diligent effort to make the personal service, the person may make service by posting a copy of the summons and the complaint in some conspicuous place upon the premises. In addition, the plaintiff shall mail, no later than the next business day following the day on which the plaintiff files the complaint, a copy of the summons, or, in the event that an alias summons is issued, a copy of the alias summons, and a copy of the complaint to the defendant at the premises by postage prepaid, first-class mail.

(3) Personal service or service by posting shall be made at least seven days before the day for appearance specified in such summons, and the time and manner of such service shall be endorsed upon such summons by the person making service thereof.

(4) For purposes of this section, "business days" means any calendar day excluding Saturdays, Sundays, and legal holidays.