[Dr. Franklin]

For a citizen, no. Which is to say they can do it but they won't.
They will do it for a court order. Doubt you could get one though.

If needed, I could well ask for a court order to track the letters. If the USPS delivered the letters, and some worker in a government office then destroyed them, that's a crime.

[Harmless Teddy Bear]

If you can get a court order they can track it.