Job Alert System

I inherented a Job portal developed in CI 2, so I started learning to use CI two months ago. I've done extensive rework of the platform, now I would like to have a job alert system where a user can search for a keyword and save the search to receive email alerts when ever jobs related to the saved search keyword (S) is/are posted and enabled. I'll like to know how the experts in the house would go about solving this. Thank you.

Ojchris