Relevance is a given, timeliness is the trick
If you were to outline these two best practices in a Venn diagram, a clear overlap is visible since in certain instances timeliness is a function of relevance. However, the overarching concept of message relevance should be a simple given and we are wasting our time trying to hammer it home. For the e-mail marketers that made the leap of faith over the anthill of relevance, timing is the next frontier that needs to be tackled to increase ROI.
Despite the advanced timing features e-mail service providers (ESPs) offer, e-mail is treated like other mass marketing media by marketing executives. If you don't believe me, just ask any CEO of an ESP about the percentage of their clients who use their timing features. I can promise you an uncomfortable look on their face will emerge when you bring the subject up. If the main objective of commercial e-mail is to sell (widgets, ideas, relationships, donations, etc.) then a message's timing trumps most other best practices yet difficult to implement.
All top sales people will tell you the calendar is their best sales tool because it ensures timely follow up around specific purchasing cycles. Top sales people know that being in front of the customer at right time is far more valuable than frequent and blanketed calls. Therefore savvy e-mail marketers have learned from their sales counterparts to view time as a holistic window into their customers' needs, timing campaigns according to specific dates, relationship cycles and behavior instead of obsessing over the right time of day to send e-mail.
Timing e-mail based on dates is the easiest for marketers to accomplish however they need to think past birthdays and client purchase anniversaries. There are so many hard dates that affect a consumers purchasing behavior aside from their birthday. Timing consumer relationship cycles are a bit harder than timing dates and requires in depth research to understand why and when purchasing decisions are made. At the top of the timing pyramid is behavior. If a marketer can master the complexities of timing behavior they are sure to reach e-mail marketing nirvana.
Even though technology makes it easier to implement campaigns based on timing quality research is needed to be successful. Timing is a science that takes a combination of primary and secondary research compiled, well, over time. Timing is so valuable in marketing (especially e-mail marketing) that only its counterpart can shadow its importance is money.