Had a great time playing this!
At first I didn't get that there were more messages than the base 4/folder shown, so I was super confused and thought I should find the information from only these emails. After I read here a bit and figured out there were more, I eventually found the codes without using the "cheat".
I was a bit disappointed that I couldn't find any easter egg (searched for : easter, egg, ludum, dare, jam, delivery (maybe cat email was one?), velvet, lobster). I also wish we could find more foreshadowing of the ending in the emails, but from what I've read it's not a topic that's ever mentioned.
It's a shame that the ending doesn't differ if you send the right code or not, the first time I thought I had figured the code out I was wrong.
I actually think the amount of ways to get to the codes is very reasonable to keep it both feasible and challenging, and the music is perfect for the atmosphere.
Great job, super original entry!