I found the answer (sometimes, due to the grand importance we attach to events, we forgo the simple truth that doing research helps save others' time...).
According to CIC http://www.cic.gc.ca/english/helpcentre/answer.asp?q=028&t=4:
[size=10pt][size=10pt]How can I check if my application has been received?
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If you mailed your application to CIC, you may wish to use a courier service that requires a signature when delivered, gives you a delivery confirmation and/or allows you to track your package. Please note that there may be a delay between the date CIC physically receives your application and the date it is opened. CIC cannot confirm that your application package has been received until it has been opened in our offices.