One of the crucial decisions to be made when running email marketing campaigns is when during the week to send out your newsletters. With so much focus on the 'to', subject, and content of emails, timing is a factor which is easy to overlook.
So what makes for good timing? It really depends on whether your emails are business-to-business (B2B) or business-to-consumer (B2c). If they're B2B, then there are a couple of rules around which there is broad consensus. Firstly, you should not send on Mondays or Fridays. On Mondays, inboxes have not been checked since Friday and are therefore pretty full. People are more likely to be ruthless when it comes to deletion. And on Fridays, people are too busy looking forward to the weekend and being able to finish work to be that responsive (and they may not even be there - there will be many who take Fridays off). The other rule is not to send overnight. Again, there is a problem with inboxes being full with other emails in the morning, but in addition most SPAM is sent overnight. Your email might be mistaken for it.
Between Tuesdays and Thursdays, and regarding time of day, there is less consensus. Some will argue that Thursdays are the best, as people have begun winding down towards the weekend and are therefore more responsive. But seems to run opposite the reasons I mentioned earlier for not using Fridays. Tuesdays and Wednesdays are likely to be the safer bet. And what about time of day? Well, between 10 and 2, when people are not dealing with full inboxes and may have the time for a quick coffee break or lunchtime read, are often regarded as the best times to send.
If your emails are B2C, then timing depends much more on what you are trying to sell. In this case, Fridays and weekends may be much better times to send, for obvious reasons. Sunday evenings is when the largest number of people are online - although remember that this might not make them more responsive. On Friday evenings many will be in a good mood - although you have to catch people before they go out. Think about who your market is and when they will be interested. There may not be a set perfect time - it could be subject to seasonal change depending on the industry.
Mark Brownlow suggests some interesting innovations with email newsletter timing, such as sending emails at the time that the person registered for the email. However, as is pointed out in a comment, this might be putting too much long term emphasis on one event. People's behaviour changes, and it is vital that you adapt.
As with all things, it is important to test what works for you. Try different times, and see the response rate. Do split-testing of your newsletter. Remember to keep updating your research and responding to changes in behaviour. If too many other firms agree with you that a certain time is the best one to send, then inboxes may fill up then and your response rate may go down. You therefore have to balance the need to build trust and expectancy by sticking to a regular newsletter time with the need to keep ahead of changing behaviour. And remember; although perfect timing is good, getting your email read is only the first step.