A couple of weeks ago, I was standing in line during visitors' hours at Suzanne Kays (the minimum security jail). I noticed that the zip code for the address for prisoners' mail was wrong. It should be 75266 but it had 75222. The address is taped up on the glass window labeled Information.
Since the mail goes to a post office box, it isn't going to get there if the zip code is wrong - I had found this out the hard way when I sent my first letter to James, as the wrong address is also attached to the DCJ visitor's handbook.
I pointed this out to an employee and all I got was a dirty look. Then the employee proceeded to give the wrong address to someone who had attempted to visit someone, but had been turned away as the inmate she wanted to visit didn't know about completing visitors cards. (Generally, if an inmate hasn't recorded details of potential visitors, he isn't going to be allowed visitors.)
So when the would-be visitor mails the letter, she should get it back in about 2 weeks. Like the first one I sent.