What is the best time of day to send email? That particular question is one that marketers have been asking since the dawn of email marketing. And, inevitably, someone would answer. It doesn't really matter what the answer was -- all that mattered was that someone said it. This single act officially turned it into the worst time of day to send email, as every marketer subsequently began sending their messages at the same time. The question subsided publicly for a while, but as deal-of-the-day and flash sales businesses flourish, owning a moment in the inbox has become ever more …

Since May we've been seeing more evidence that ISPs are gaining confidence in their use of engagement data. This is a trend we've watched closely, because bulk delivery decisions based on user behavior can make reaching the inbox even harder for lots of mailers. Last week we got confirmation that engagement data has become a far more prominent component of deliverability at one major ISP: Yahoo.

It's the end of July, and for those of us in email marketing, the time to start thinking about the holiday season is while the summer sun is still blazing. While many holiday trimmings are the same each year, the world of email marketing leaves little room for recycling our holiday "traditions." Sure, we might add gift services footers and touches of holiday flair to our headers each year, but much of our strategy must respond to the demands of the season while keeping our eyes on the opportunities developing beyond the inbox. So what's different in 2012, and how …

In my previous column -- "Are You Ready for a Mobile Subscriber Base?" -- I relayed several mobile research statistics that make the case why email marketers can no longer ignore designing and optimizing their emails for a growing mobile subscriber base. I also outlined some implications of these statistics and high-level tips, such as taking a mobile-first approach and designing for touchscreens navigated by fingers. Now I'm tapping the know-how of my four favorite mobile email-marketing optimization experts for advice on optimizing emails for mobile devices.

Last week I participated in a webinar with an email marketer who said in her presentation that her company sends as many as three emails per day to some of its subscription lists. Almost all of the questions during the audience QA that followed were variations of, "How do you do that? Can you teach me?"

The thing about great strategies and approaches to the email channel is that they are very specific and unique to a brand, or even a product line - they don't necessarily translate across every vertical or even brands within a vertical. Your email program and its success is as unique as the swirls and loops on your thumb. However, the premise of great email is very similar, but daunting: Give your subscribers what they want.

Marketers know they should test, but it's easy to get in a rut testing the same things over and over again (e.g., subject lines). The following is a personal list compiled and modified over the past 10 years. Not all of these will be relevant to your program. And some of them are more likely to have a significant impact on performance than others. Take a look and see if any of these present new opportunities for you to test and improve your email program.

Expectations are steadily rising in the inbox. Having permission only gets you so far nowadays. Irrelevant and unwanted email is the new spam in the eyes of both consumers and ISPs. Everyone agrees that "relevance" is the solution, but it's often discussed in vague, mystical terms. While relevance is indeed in the eye of the beholder, that doesn't mean it's indescribable. Relevance comes down to a mix for four factors: emails being (1) desired, (2) user-friendly, (3) valuable, and (4) open.

I recently spoke with someone who said his company had four billion email addresses, of which two billion had name and addresses associated. Considering the U.S. population was 313 million last time I checked, this really made me think about the industry and what we've become.

Most "mocial" (mobile/social/local) email conversations have been about the impact of social media and networks. Participants range from the misguided, who suggest that social media would kill email, to folks like yours truly, who believe that the two channels actually can support each other and make each other more relevant. Social networks and media have had little serious impact on email marketing. The mobile aspect of the mocial trifecta, however, looks like it will have a monumental impact on our beloved channel.