Iran: How do Iran track citizens going to Syria?

The Letter N says: “If you are an Iranian citizen who wants to go to syria, you need to go to the nearest Iranian Embassy, which then gives you an official letter saying in effect : “so and so is our citizen, please give her a visa” ^[1]. It is a formality, of course, which was most likely set up to allow both the Syrian and Iranian governments the ability to track their nationals who enter their borders from a third country.”