Working heavily with email templates lately within MailChimp, I came across some weird behavior. The iOS Gmail app was just making things look completely different than every other email client. At this point I knew that a lot of stuff didn’t work with Gmail but this had me scratching me head. After some research I discovered that this was due to Gmail adjusting the email font size for a better experience by increasing readability. In the case of my template design, this was not desired.
Putting a hidden div filled up with a bunch of non breaking spaces into your email template prevents this font resize. In the code below there is just enough of them that it creates ~ 500px area which is enough to prevent a resize.
<div style="display:none; white-space:nowrap; font:15px courier; line-height:0;">
</div>
Ironically enough, this snippet was taken straight from a Google Analytics email.