I note that this thread is almost two years old.

While I do not know the size of the T4 collection box, I do know that many USPS blue collection boxes have since been retrofitted with very small slots designed to foil thieves who "fish" for mail from such boxes in hopes of finding cash, washable checks, or credit card numbers in envelopes contained therein. So I think it unlikely that the collection box in T4 would be able to accommodate a package of the size described by the OP.