The most fleeting joy in this world is that of sending off an important email, as it's inevitably replaced by the anxiety of waiting for a reply. If you want to get a quick reply to your email, send it in the morning.
Screenshot: Warner Brothers
Brendan Greenley, data scientist at the email scheduling company Boomerang, explains further in an email to Lifehacker:
The best time to email someone is at the start of a work day, as people tend to get through emails in a last one in, first one out (LIFO) method, first reading and replying to messages at the top of their Inbox. Boomerang's research has shown that people tend to write the most emails on weekday mornings before noon.
If your email reaches your recipient's inbox between 7AM and 9AM, it will likely be among the first emails they see before this key window of time when they are most likely to write emails and replies.
Boomerang's findings (pulled from a database of over one million public emails) match those from a Yahoo Labs/University of Southern California study of over 16 billion emails. The Yahoo study found that people replied more quickly to email between 8AM and noon (and early in the week).
Sending outside those times can get your email buried under the morning rush, then ignored for days despite your recipient's best intentions. So whenever you send email, if you want to prioritise a quick reply, use a tool such as Boomerang or cloudHQ's Schedule Email to schedule its delivery for the morning - or whenever you've found your colleagues tend to answer their email.