Idaho Code § 6-304: Service of notice.

The notices required by the preceding section may be served either:

1. By delivering a copy to the tenant personally; or,

2. If he be absent from his place of residence and from his usual place of business, by leaving a copy with some person of suitable age and discretion at either place, and sending a copy through the mail addressed to the tenant at his place of residence; or, if such place of residence and business cannot be ascertained, or a person of suitable age or discretion cannot be found there, then by affixing a copy in a conspicuous place on the property, and also delivering a copy to a person there residing, if such person can be found; and also sending a copy through the mail addressed to the tenant at the place where the property is situated. Service upon a subtenant may be made in the same manner.