code to be executed automatic on server

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C#

I am creating a c#4 windows application.

This application creates work team meetings & then sends email to work team members.
Database is published on the internet not local because this application will be accessed from different people.

My problem is when someone creates a meeting he may say it'll repeated each week.
So what I need is to add new rows in the database for each meet week. But the problem is that I can't do that from my application because I don't know when the application opens. Maybe someone opens the appliction, creates a meeting and then closes the application & didn't open until he want to creat new meeting.

So i need something that works on published server that do that work, check if new meeting is near and send an email to members & add new row in database.
So i need code that runs automatically on server that checks every half hour if there's new meeting to do.

How can i do that?
Anyone help please.

Edited for grammar and spelling