The French Post Office can help you in two ways: most have an ATM where you can obtain cash with your ATM card, and you can mail things here. The closest Postes for Conde dorm residents is at the north east corner of the Odeon square . In recent years, the La Poste has been streamlined with lots of prepaid envelopes and boxes. Often the best deal for a letter or postcard is a pre-stamped international envelope sold by the post office. You can also purchase make-it-yourself boxes for various weights for international mailing. La Poste is open 8AM to 7 PM Monday through Friday and 8 to noon on Sat.
Both of the ESA dorms have high-speed wifi connections. At the Condé dorm, there is one wifi password for all users (dorm residents and ESA participants). At the Ste. Famille dorm, there is a unique wifi connection and password for each floor, as well as one available for visitors.
The city of Paris also has free wifi throughout public parks. Service can be spotty, however, and a bit slow. It's best to be near the "borne" (wifi station). See a map of service by clicking on the map linked on the right.
If that's not enough data, or if you need to access wifi all the time, you might want to explore some pocket wifi providers like TEP, HipPocket or Travel Wifi.
With the advent of cell phones, the dorms dropped their phone lines and expect you to use your cell or computer to communicate.
You should check with your carrier about charges for using your phone overseas. Some carriers have free data plans for international travel (but you have to pay for phone calls). Others will provide a limited number of phone calls but charge you for data. You may wish to inquire about purchasing a one-month international plan to avoid unforeseen surcharges when you return home.
Very common these days is to setup an eSIM on your phone and purchase a 1-month data plan. HERE is a good video that gives an overview and some recommendations.
We encourage you, too, to check your phone, iPad/tablet and computer to make sure you aren't accessing data you don't need. This usually involves turning off Data Roaming and Location Services. The New York Times recently published an article with advice for traveling abroad with your smart phone. Apple has a help article on traveling internationally with an iPhone and iPad. Or read this article on data and international travel.