There’s been a good deal of discussion lately about the visibility and value of a Facebook or a Twitter post. It turns out that a Facebook post has a “shelf life” of approximately 18 hours: If your intended target hasn’t viewed it by then, chances are he or she won’t end up reading it at all.

For Twitter posts, the “useful life” is even less. Generally speaking, once your Twitter post scrolls off the viewing screen due to more recent posts coming in, it’s likely never to be viewed.

But what about e-mail messages? Seeing as how they’re targeted specifically to their recipient, surely they’re more likely to be viewed even after a lapse of time, correct?

Yes and no.

To some degree, the dynamics of an e-mail message means that recipients see them as “important” in the way that a Twitter or Facebook post might not be.  However, with the plethora of e-mails being sent by retailers and other vendors – something this cheap to do is usually worth almost as much as it costs, after all – people have become less prone to view all of their e-mails.

GetResponse, an e-mail marketing firm, has also found that timing is a significant factor that affects open and engagement rates for e-mail marketing campaigns.

GetResponse researched e-mail campaigns covering the 1^st Quarter of 2012 to determine how the time of day affects open rates. It found that two factors have the most influence:

• When the e-mail was sent
• The amount of time that elapses from when the e-mail is sent to when the recipient checks his or her inbox

It turns out that morning e-mail deployments are most popular for senders (~39% of e-mail campaigns are deployed in the morning), while afternoon deployments occur in ~26% of the cases and ~30% are deployed in the evening. (The balance happens between midnight and 6:00 am).

Interestingly, GetResponse found that “morning” opens and clickthrough rates are actually somewhat lower than those sent at other times of the day – particularly in the afternoons: Top e-mail open hours are 3:00 pm and 4:00 pm and top clickthrough rates are at 3:00 pm and 8:00 pm.

These results, coupled with the fact that more sending activity occurs in the mornings, would suggest that deploying in the afternoons would be better for engagement and to “avoid the noise.”

GetResponse surmises that the volume of e-mails deployed during the morning hours makes it more likely that recipients skip over a bigger portion of those e-mails.

But another key finding from the research is that an e-mail message is most likely to be opened within one hour of delivery (~24% of the time).

Within the second hour, that open rate declines by half, and by the third hour, it drops by an additional 30%.

By the time the fifth hour is reached, virtually no new open activity is being recorded. So it’s safe to conclude that e-mail engagement behavior isn’t really all that different from what happens with Facebook posts.

There are a couple of takeaways from the GetResponse research. Vendors should consider making afternoon deployments in addition to ones in the morning.

Also, in order to increase the likelihood that e-mails are opened within the first hour of receipt, stagger deployments by time zones (including international recipients) to conform to the best times of the day for engagement.

In the end, does getting e-mail messages into inboxes during the most receptive times for engagement make that much of a difference?  GetResponse’s conclusion is that it isn’t inconsequential:  Average open rates and clickthrough rates can be lifted by ~6%. 

On the margins, that’s pretty decent.