Responsive e-mail template

"Responsive Emails" is not going to be a Kentico thing, it's going to be a browser / email client thing. It's very hard in general to get email templates to show properly on all email clients and browsers, not all support the various styles needed.

https://www.campaignmonitor.com/css/

This provides a good list of what you can and can't use depending on your targets. Once you know what styles you can use and what HTML, then it's just about adding that to your email template HTML output.

In Kentico 9, none of the emails are responsive. With a website, making it responsive is the responsibility of the developer. The same is true for email html templates. They are html and css markup you create. So best to have someone who knows about the different "gotchas" with emails and clients, then use something like http://litmus.com/ to see what they look like in email clients. There are also companies which will take your design and make them responsive if you don't have anyone on staff.