Recently, we explored how starting your emails with one specific word, or closing them with a simple three-word phrase, makes people more likely to reply to them.

Those reports were based on a study of 300,000 emails. But now there's a much larger study, one that examined hundreds of millions of emails, and came up with another important piece of the puzzle. 

The big takeaway this time is simple: Send your emails at a time when fewer other people are sending them.

Statistically, that means your sweet spot is likely Sunday evenings.

"The closest to a 1:1 relationship where you receive one reply to every outgoing email you send is Sunday," wrote Elise Musumano at Yesware, the email application company that conducted the study.

That research actually bears out an earlier, more detailed study that Yesware conducted (albeit one that examined substantially fewer emails--about 500,000, focusing on sales emails).

Open-and-reply rates were markedly higher on the weekends than during the week: a 45.8 percent reply rate overall, versus 39.1 percent during the week, across all emails.

Moreover, emails sent in the early morning or the early evening--more specifically, between 6 and 7 a.m., or around 8 p.m.--had very solid reply rates: around 45 percent.

That same study found that there's really no difference in terms of response rates during the week: They're all uniform--and thus uniformly inferior to weekend email send-and-response rates.

So, to summarize everything we've learned and written about emails in the past few days:

  • Open with a short, direct, informal greeting. "Hey" seems to work best.
  • End with gratitude. The three-word phrase "Thanks in advance" had the highest response rate.
  • Save your important emails for the weekend, if possible, when there's less competition.
  • If you can swing it, send emails between 6 and 7 a.m., or else around 8 p.m.

The study didn't break down whether to consider the sender's or the recipient's time zone if they're not the same. But given advice we've seen elsewhere to know your audience, it makes the most sense to time it for your recipient's time zone, not yours.