Your inmate can write back through InmateAid even without your personal address. The return address printed on every postcard and letter sent through InmateAid is the company's Florida address, not yours. That address is right there on the envelope your inmate receives, and it is all they need to send a reply.
When your inmate writes back to that address, InmateAid receives the letter, scans it into your account, and notifies you that a reply is waiting. You log in and retrieve it from there. The whole exchange stays private on your end because your home address never enters the picture at any point.
That system works in both directions by design. You send without exposing where you live, and your inmate replies to a stable address that routes everything back to you securely. It is one of the more practical features of the service for people who have safety or privacy concerns about their location being known.
If you have not received a notification about a reply yet, make sure your account email is current and check your spam folder just in case. Once your inmate sends their letter to the InmateAid address, the turnaround on getting it scanned and into your account is typically quick.