Time Traveller

In this challenge, we are told to find an email address that was shown in the NASA’s website (nasa.gov) on December 31, 1996.

The way to find something in a certain date is going to web.archive.org (WayBack Machine):

Here we search for nasa.gov and get a lot of snapshots of the webpage. Curiously, the oldest snapshot is from December 31, 1996:

If we check this snapshot, we see some information. And here we have the email:

So, the flag is CTFlearn{today@nasa.gov}.