Just my experience with all kinds of email accounts on iOS but it's always a good idea to just delete all email accounts before a major iOS update, then update, and then add them back.
This advice applies unless of course you are still using POP email (in that case the 1980's is calling and wants it's protocol back)!
Adding your "cloud" accounts (IMAP, ActiveSync, WebDav, Exchange, etc.) back after a major iOS update tends to let them work as tested by the Apple dev team. It only tales a second and typically gets things working correctly immediately.
Lastly, other that iCloud (purely for Find My iPhone), consider setting all of your email, calendar, and contacts accounts to "Fetch" instead to greatly improve your battery life.