Sample eMail is not responsive in mobile device
Hi. We are new to Marketo and are finishing up our first email. When I view the sample email I send to myself in the Gmail app on my phone (iPhone), the email is not responsive. So, text that is in three columns does not stack like it does in the responsive preview mode in Marketo, rather, it is on one row.
How do we make the email be responsive? Is this a Marketo issue, or an issue with our template?
Preview in Gmail app:

Preview in Marketo, Phone view:

For reference, attached are screenshots showing how it looks in the Gmail app and in the Marketo phone preview.
Thanks!