The official USMC OCS Facebook page also sends out messages.
I got this yesterday:
"Good morning, candidates have sent letters home with their correct mailing address and platoon assignment, you should be receiving those letters soon."
The parents of my DS' college roommate got their letter on 5 June. It was postmarked on 2 June. They arrived at OCS on 27 May.
If they are actually required to send addresses, we should be getting ours in the next couple of days.