Outlooks for windows is showing the mobile template on desktop and android variations of outlook are showing the desktop template on mobile. Mainly,
  1. columns are being modified, and
  2. the width of the email is not matching the set values (~500-600x)
Customer is comparing columns against their prev experience with mailchimp. Here's a litmus test of a mailchimp email with multiple columns, rendering correctly on all clients: https://litmus.com/folders/unsorted_emails/emails/15125535/checklist
Comparing the two, I noticed that in the mailchimp version, the body width is static, set within a table in the html. Meanwhile the unlayer email expands the full width of the desktop window, despite only have 1 column in the rendering.