They don't have to acknowledge it per se - in fact, they won't. I suggest that you courier the package to CPC-Vegreville by Purolator, FedEx, etc. They can tell you how long it will take - I think Purolator is 2 days, and FedEx can do overnight, but you've got enough time that you don't need to pay a lot of extra $$ for fast delivery. Still, DO get delivery confirmation . . . that's important. You'll pay a bit more money than standard mailing but, as long as they receive your ap before your status expires, your confirmation of receipt becomes your proof that you have legal temporary status between the time you submit the ap and when you get AIP and your OWP is issued (4-5 months). Not only that but you'll have peace of mind from knowing that your application actually arrived safe and sound. Remember, you're not going to hear a word from Vegreville for at least 4 months - probably more.