what was so special about the last message sent by sebastian shultz to michael.

The mail that Michael got was from the real Sebastian. 

it was the real letter .... other letters were from printer ....

The last message was full of emotions.Sebastian thanked the narrator for taking so much pain to rescue him in every game.He also says to keep the visor and the games as he deserved it.It was a message from the real Sebastian.

The thing was that earlier Michael was getting virtual  messages were sent by virtual  Sebastian through printer but in the last message real Sebastian sent real message onto his email.

Real seb

The last message was sent by the real sebastian shultz who have recovered from the coma. He thanked Michael for saving him. The message was full of emotions and shultz told that they could meet up soon. He also tell Michael to keep the games and computer as he have earned them

Hope this helps you :)