Email The Register Of Ecommerce
Email out performed all other channels when I was an Ecom director. Email contributed more margin to the bottom line and was the cash register of other "lost leader" channels such as PPC. 

Email also creates important diversification. People on YOUR list put you in control at least as far as you don't irritate or spam. If more than a tiny group on your list complains you are marketing insensitive to their needs (spamming in other words) and your ISP will black ball your website and it can be hellish to get off. 

Email As Mobile Life Curator
Email marketing is not without its new challenges. Batch and blast the same message means conversion will go down as spam complaints go up. Email's role is changing with the dominance of smart phones.

Smart phones and pads are the easiest way to manage emails. Email deletion is easiest on mobile and mobile fills up the free time of waiting in lines and sitting on the subway. Wonder why your open rates are going DOWN? A: Smart phones. 

All of this means you need personas and segments AND responsive emails in your email marketing these days. You MUST create relevant messages. Use personas, fully articulated archetypes for between 3 and 7 "super groups" within your list. 

Know what segments within your list such as "multi-buyers" or VIPs are the most profitable. Combine personas, which THEY ARE with your financial segments what THEY MEAN to you to create campaigns that will appeal to THEM and make money for YOU. 

Email Marketing In Mobile World Tips
* Subject Line is beyond important.

* Create responsive email (email must look great on all devices).  

* Use PERSONAS and SEGMENTS together.

* Tell STORIES over TIME.

* Curate User Generated Content INTO your email marketing.

* Count and trend unopens as a NO.

* Create & Trend new KPIs such as $ / sent, $ / opens.

* Keep emails OFF your website (dupe content and hurt heuristics).

This last bullet needs some explanation. Your email marketing needs a "can't see this email view it here" link, but keep your creative in a NON-SPIDERED folder.

Allowing your emails to get spidered can cause duplicate content problems and the heuristics of your emails don't help since, if you are creating great Call To Action emails, your audience will not spend much time on your emails as they are simply attention getter pass through to points of conversion.