With the advent of iOS 11, designers are reporting wierd quirks with their design when opened in a device running the latest operating system, particularly when it comes to zooming or right vertical gaps in the email.

One of the first things you should try if this happens is to add this tag to the head of your email.

<meta name="x-apple-disable-message-reformatting">

This technique disables iOS’s “auto scale” capabilities and was actually suggested by an Apple engineer James Magahern
(h/t @hteumeuleu).