User initiated notifications

Hello,

We are looking for a solution for our members.

We need a trigger for a certain post type, the user needs to give in his keywords where he wants a notification on.

When a post is placed with that chosen keyword, we would like to send email to user.

We are running a car dealer website (members only) and would like the dealers to get notified if they want that on certain keywords. Like Mercedes orso!

Hope somebody can direct me how to do this!

The page I need help with: [log in to see the link]