Denver International Airport pneumatic tube systems
According to the Public Relations Department at the Denver International Airport, as of May 24, 2019 there is no such pneumatic tube system at the airport.


  Hello Juan,
  
  Thank you for contacting Denver International Airport. We have
  evaluated your email. I spoke with airport operations to find out if
  they had any information on using a pneumatic tube system and they
  advised me they do not. We do appreciate your feedback. 
  
  Thank you, kindly, for bringing this matter to our attention. 
  
  Warm Regards,
  
  Flydenver Team  Meseret