Even as I was typing this request for help, I kept trying my program again, hoping that the problem was temporary. Just a minute ago, I ran the program and got back some real data. However, I still don't understand why I got a 302 error - in my perl script, I attempted to post to:

http://www.usps.com/cgi-bin/zip4/zip4inq2
[download]

During those times that the script was yielding a 302 error, I could still go to USPS.com, fill out the form, and, when the results came back, the URL would show:

http://www.usps.com/cgi-bin/zip4/zip4inq2
[download]

so what was the catch? Thanks in advance for your help.