Important.txt is a found on WHOIS by Louis. The text file is written:
Had contact with admins and I should not add the following servers to the WHOIS: 255.0.255.0 251.153.56.29
The riddle obviously points to the NPCs 255.0.255.0 and 251.153.56.29 and is probably the easiest riddle in the Riddle Trail.