My 6S Plus and now 7 Plus the text on the mail app is very small and hard to read. Not on all emails but some. I never had this issue on iOS 9 the text was always enlarged to read. Appears to be an issue with the Dynamic text. Anyone else?
The typical troubleshooting for this from past thrashes has been to try to exit and close the Mail app and launch it again, restart the device, and/or try changing some threading options in Mail settings.