I recently upgraded from the latest version of IOS 9 to IOS 10.1 and discovered a possible problem for low vision users like myself who use a mixture of voice over and vision. The problem I will describe did not occur most of the time with earlier IOS versions. Also, when I addressed this issue during a phone call over the weekend wht someone from Apple Accessibility, the call center had already received just a little over 40 calls from others experiencing the same thing.
If you have set your text size to a desired font, it will not necessarily appear in that desired size when viewing email. In my case, at least, most of my emails now have print that is extremely small. Only the occasional email will still have text in the desired font size. So I either have to cut voice over off and use the pinch gesture to expand the size of the print as someone with full vision would do, or I copy and paste the body of the email into my Notes app where the size of the font displays at the desired size. They are work-arounds that I can live with, but I would hope that Apple can address this problem since it did not exist (at least for me) with prior IOS versions.