There isn’t much information on their “Free Services” page:
You can buy stamps at the Maison de la Presse newsstands, and you will find mailboxes in the public area of the terminal.
Their airport map, while good, doesn’t identify the drop box locations.
The mailboxes are pre-security, most likely on the departure floor.
Robert noted that there is a mailbox located across from the American Airlines ticket counter.
Note: Canada Post mailboxes are typically red.
Last Updated 22 November 2021