In my experience - sometimes and / or never! I've got 2 speeding fines on my car and 2 on my wife's and we've never had a SMS. I only found out after I went on the Metrash website.

However, when I got busted for parking on the pavement at the Souk, I got an SMS within 5 minutes of the ticket being issued.

Probably best to just check on the website....