Yes, they send all the messages through emails that you provide in your initial application. Only the Medical request will come through USPS. And if you change the address while in progress, they will still send you in the same old address that you first provided  in your initial application. I tried to change my address in their system like more than 10 times, and they still send it at old address. So check that too. 

Check your spam, many forum members in canadavisa.com were saying that their email ended up in spam and they came to know about it  after a while. 

Goodluck with your process. Wait ....... everything will be just fine. 

cheers.