Extremis

Extremis was the subject of an email that the virtual construct of the Twelfth Doctor sent to himself in the real world from a simulated world created by the Monks.

History
Within a simulated world created by aliens called the Monks, there existed virtual constructs of most people on Earth, including the Twelfth Doctor, Bill Potts and Nardole. When the Doctor was sent to the Vatican by the Pope, he began recording the events with the sonic sunglasses, since this version of the Doctor was blind too. After Bill and Nardole were deleted from the simulation, the Doctor sent the email to his counterpart to warn him of the Monks' intention to invade. (TV: Extremis)