E-Mail persists after many decades and will continue to survive Chat, Skype, etc. - just as roaches have survived the atomic bomb. Despite being a pest, E-Mail is also an effective marketing channel and the most personal communication you have with your users and customers.
You've survived Gmail's spam filter. Now let's make sure you also survive mobile devices with responsive E-Mail HTML. It's not as difficult as you think. Let's examine how developers have solved common problems with tried and true techniques for designing and developing bulletproof E-Mails.