If you want to make sense of what you just saw you can hit the jump for one possible explanation.
It’s about how time/the universe corrects a paradox. Each time the letter is delivered - a letter that should be written in the future - a paradox is created. Time/the universe starts getting more and more agitated by it, for lack of a better word, until it finally reacts strongly enough to prevent the paradox from happening again. This is also why the specifics of the letter are not important. It’s the fact that the letter exists before it should that is the real matter of importance.
Basically, the story is that paradoxes are not allowed. The universe will make sure to correct them. Somehow. That’s why there were no more videos after the wine was spilled on the letter (and before she could memorize it).