Apple's new operating system won't work on older models of the iPhone and iPad and is causing problems for some people using the Mail app.

iOS 11 was released overnight in New Zealand and comes with a suite of new functionality and design features.

iOS 11 will be available on the trio of new iPhones released last week and be compatible with the following models of iPhone, iPad and iPod:

iPhone: 5s, 6, 6 Plus, 6s, 6s Plus, SE, 7, 7 Plus, 8, 8 Plus, X

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iPad: 5th generation (2017); Mini 2, 3 and 4; all Air models and all Pro Models

iPod Touch: 6th generation (2015)

If you own an iPhone 5 and iPhone 5c you will not be able to get iOS 11. Apple is also dropping support for the 2012 iPad 4.

A problem with sending and replying to emails from your Microsoft Outlook, Office 365 or Exchange email account using Apple's Mail app was discovered.

The updated Mail app is not compatible with the Microsoft Outlook platforms.

Microsoft said it was working with Apple to resolve the issue, but advised people to download the Outlook for iOS app until a fix was found.