Hi,
rjo98's question is absolutely legitimate and I find that most of Dah-veed had to say was totally preposterous at best and of bad faith at worst. On the iPhone5 (6.0.2), here's the situation:
1. I can lock "myself" out e.g. of Safari - the icon simply disappears, and to bring it back I must give my code. This implies two things, namely
- Apple does know how to do that triviality, but just wouldn't for Mail
- Apple does want me to share my "personal" device with others (e.g. my family)
2. I can NOT do the same for Mail
3. All the recipes proposed above do NOT work for professional (i.e. NOT Gmail etc.) mail, because disabling the account really makes it disappear altogether and I need to input all the settings (server etc.) again to access the account - too much of a hassle
4. No third-party app that would offer the functionality seems to be available (and I would be willing to pay!) which, given the huge popular demand, means they must have all been blocked by Apple.
All of which simply means Apple do NOT want the Mail protected in ANY reasonable way on these devices, and the only reason I can see for that (if we put aside the idea they really want to offer a bad product) must be what Quilps2 said above, namely that they hope your wife and children will force you to dish out for more of the stuff. And sadly, it also means that asking Apple for the functionality will go nowhere (sorry for the Hope, it just died).
So the only interesting question that remains is whether this might backfire on Apple or not. I have to say that the iPhone is a nice device... but for THIS SINGLE REASON I have already recommended Androids for my emplyees.