I found this works for me as well, just targeting the div wrapping the button doesn't work in Outlook.com, gotta target the button too!
Just to flag for you, if you use fluid images (don't rely on MQs to make them responsive) and normally don't add a
height attribute to them, Campaign Monitor will add it in when replacing an image.
I flag this because it used to be an issue with the Gmail app (it would change CSS
height: auto; to
min-height: auto; and therefore wouldn't override the
height attribute) previously. It's not an issue now with Gmail, though I know it was also an issue with Yahoo app — not sure if it's been fixed or not but it would do the same as well. This results in the images looking squished as the height won't scale proportionately.
Definitely Hybrid with media queries layered for progressive enhancement! IMO it provides the best base to work off of, and you know that if media queries are not supported, that the email will gracefully fallback to a still responsive email, but just not with all the bells and whistles that can be added with the media queries.
Highly recommend this tutorial on Hybrid development: https://webdesign.tutsplus.com/tutorials/creating-a-future-proof-responsive-email-without-media-queries--cms-23919
I don't believe it's specific to Nougat. See this post: https://litmus.com/community/discussions/6012-outlook-com-email-app-no-longer-responsive-android