This outdated version can also cause some negative effects on the iPhone's ability to receive mails from the server regularly. You need to know that outdated system can reduce the ability or features of your iPhone device significantly. When you don't update your firmware on your iPhone device regularly, you may have outdated version of your iOS system. Outdated Version - Although this problem may be uncommon for most people, you should never forget about this issue.Make sure that you have fast and stable Internet connection to get access to all mails from your email account. Network connection is very important to ensure that your device can get all emails that are stored on the server easily. This network problem can be caused by broken network connections from mobile network or WiFi connection. When your iPhone 6s cannot get access to the Internet, you should never be able to get access to your email account and all available new mails. Broken Network Connection - This is considered as one of the most common factors that can cause email problem.7.5 Can't Find Camera Roll on iPhone 6S.4.5 Is Camera 360 Compatible with iPhone 6S.4.4 How to Turn iPhone 6s into a Spy Camera.4.3 How to Take HDR Photos with iPhone 6S.