email vs letterbox

email

noun
  • A message sent through an email system. 

  • An email address. 

  • A system for transferring messages from one computer to another, usually through a network. 

  • A quantity of messages sent through an email system. 

verb
  • To send (something) through email. 

  • To send, or compose and send, an email or emails. 

  • To send an email or emails to. 

letterbox

noun
  • A collection point for mail intended for onward delivery, a secure box or receptacle for this purpose. 

  • A hidden container that holds a logbook and rubber stamp, found by following clues as a form of recreation. 

  • A rectangular hole or slot. 

  • A delivery point for mail, a box, compartment or slot for this purpose. 

verb
  • To transfer a widescreen motion picture to home video formats while preserving the original aspect ratio, with the placing of black bars above and below the picture area. 

  • To hunt for letterboxes (containers with logbook and rubber stamp) by following clues. 

adj
  • Transferred to home video formats while preserving the original aspect ratio, having black bars above and below the picture area. 

How often have the words email and letterbox occurred in a corpus of books? (source: Google Ngram Viewer )