During my time at a London advertising agency, I worked on large digital marketing campaigns which involved e-mails. The e-mails that were built are responsive and display consistently across all clients on mobile and desktop.
E-mail is still very much behind the web in terms of coding, e-mails still need to be built in tables, image heavy, and inlined CSS. However, as standard I was able to make the e-mail builds work across Outlook 2000 - 2016 for OS-X and Windows, all web based email clients and mobile devices. Each client has its own caveats to look out for, and after a lot of work and testing they were delivering well. It was especially important that the e-mails look was consistent across devices as some of the e-mails were going to thousands of customers at once delivering the message of the campaign.
We also developed a system based from the email framework by Zurb. Sections of e-emails have been split into modules, and templates are built and data injected using Handlebars template system.