Some interesting insights have emerged from a large-scale study of email usage undertaken by Yahoo which looked at the habits of more than 2 million users exchanging 16 billion emails over several months.

It find that as users receive more email messages in a day, they reply to a smaller fraction of them, using shorter replies (so the early bird is more likely to get the worm, as the saying goes!)

Nearly 90 percent of users replied to their emails within a day, with about half responding in around 47 minutes. Interestingly, this distribution is very similar to the time it takes users to retweet a message on Twitter, the report notes.

The most frequently occurring reply time was just two minutes.

Most email replies were very short: between 5 and 43 words. Just 30 percent of emails went on for 100 words or more.

Some other trends emerged. Emails received on weekends get substantially shorter replies compared to those received on workdays, and these replies are also much slower.

Messages received during the night get slower replies than those received during working hours. Interestingly, messages received in the morning get substantially longer replies than those received in the afternoon and evening.

Youngest email users, teens, have the fastest reply times; as users get older they become slower to reply to emails. Median reply time of different age groups was as follows: 13 minutes for teens, 16 minutes for young adults (20–35 years old), 24 minutes for adults (36–50 years old), and 47 minutes for mature users (51 and older). Gender does not seem to play as important a role in the replying

The study also looked at how people adapt to the increased information load: do they become more active and reply to more emails, do they delay replying or fail to reply altogether?

It found that email load affects user behaviour. Users increase their activity as their email load, i.e., the number of emails received that day, grows.

“While users increase their activity with higher email load, it appears that they are not able to adequately compensate for the increased load. A the email load increases, users reply to a smaller fraction of their emails, from about 25% of all emails received in a day at low load to less than 5% of emails at high load (about 100 emails a day). However, highly active users are better able to keep up with the rising email load than low activity users.”

The full report is available at http://arxiv.org/pdf/1504.00704v1.pdf