When navigating to the Settings app on an iOS device, there are three categories of setting that allow for an account to be added - either Mail, Contacts or Calendars (adding an account can be achieved by opening the respective category, tapping "Accounts" and then on "Add Account"). What isn't immediately obvious, however, is whether it's possible to remove an account from one of the above categories, whilst keeping the data synced from another - for example, I may wish to remove an Exchange ActiveSync mailbox from the native Mail app, but keep my contacts syncing from that same account within the iOS Contacts app. So - my question. Is it possible to either add or remove an account from the Mail, Contacts or Calendars section of the iOS Settings app - whilst keeping data from that same account synced within the other categories that it hasn't been deleted from?
In a word, yes.
Settings > Mail > Accounts
Select the account you want to edit/change
There will be on/off buttons allowing you to selectively sync only those parts of the account you want.
In the screen capture below I have only Mail turned on. I could just as easily turn Mail off and have any combination of contacts, calendars, reminders or notes on.