They found that the length of a reply and the number of messages sent in a thread were so predictable that algorithms could anticipate it very accurately. Younger people send faster, shorter replies, and men send shorter messages than women. Unsurprisingly, people respond more quickly to messages sent during working hours, and their responses are longer then, too. Emails tapped out on mobile devices were shorter. The more email a person received, the smaller percentage of messages they responded to, and those responses were shorter.