Cambrai Post Office is located close to the Cathedral, Avenue de la Victoire.
(Not too far also from the tourist office.)
Several services are available such as:
Self service postage
Actually closed: works until the end of June 2020
Open from Monday through Friday from 9:00 a.m through 6 p.m.
On Saturday, from 9:00 a.m. until 12:30 p.m.
Closed on Sunday.