During normal daily use, the Mail app in iOS 8.1 maintains a fully functional state if you have an active email account and your email service provider's servers are online. However, problems specific to Mail or your iPhone may cause the app to lose some functionality or freeze altogether. For example, Mail cannot retrieve your messages if your iPhone cannot connect to the Internet. Performing a series of troubleshooting steps -- such as confirming that the app's settings are accurate, updating iOS and rebooting your iPhone -- can help you to resolve the problem.
Check Your Internet Connection
Like other mobile email clients, the Mail app needs an active, persistent Internet connection to send and receive messages. When the app cannot access the Internet, it displays a message describing the problem, such as the "Cellular Data is Turned Off" pop-up message. If you have a cellular data plan, tap the "Settings" icon on the Home screen, select "Cellular" and then activate the cellular data option. If you don't have a data plan, you have to wait until you are within range of a Wi-Fi network before the app can resume exchanging email messages.
Check Mail’s Settings
The Mail app cannot retrieve your messages if your email account's settings are configured incorrectly. For example, Mail cannot connect to your email server if you recently changed your email account password, but you forgot to update the password in Mail's Settings. Tap the "Settings" icon from the Home screen, select "Mail, Contacts, Calendars" and then select the name of the account that you want to check. Tap "Account" to access your account information. From this screen, you can check your account password, email address and email server information.
Close the Mail App
If the Mail app is frozen -- that is, not responding to any tactile input -- forcing the app to close can resolve the problem. Press the "Home" button twice in quick succession to reveal the list of apps -- each app appears as a small preview -- that you recently opened. Swipe to the left or right until you find the Mail app preview, and then swipe the preview up to force-close the app. Tap "Mail" from the Home screen to reopen the app and regain access to your emails.
Update Your iPhone
The Mail app may be experiencing problems because you are running an older version of iOS on your iPhone. Apple regularly releases updates for iOS to address any glitches that may cause the operating system or apps to malfunction. To check if an update is available, tap "Settings" from the Home screen, select "General" and then tap "Software Update." If an update is available, tap "Download and Install." You can also update your iPhone using the iTunes software on your computer. It is also a good idea to back up your iPhone using iCloud or iTunes before you begin the update process to prevent data loss.
Restart or Reset Your iPhone
Similar to a computer, restarting or resetting your iPhone can repair problems that are causing the Mail app to malfunction. Press the "Sleep/Wake" button and hold it until the Slide to Power Off slider appears on the screen. Drag the slider to the right to turn off the device. To restart your iPhone, press the "Sleep/Wake" button again and hold it until you see the Apple logo on the screen. If you cannot restart your iPhone because the device is unresponsive, perform a reset -- which is the process of forcibly restarting your iPhone. Simultaneously press the "Home" and "Sleep/Wake" buttons and hold them for a minimum of 10 seconds. Your iPhone automatically turns off and restarts.
When functioning correctly, your iPhone's Mail app transmits an email message to the designated recipient after you tap the Send button. However, the Send function may fail to complete if the size of the email message exceeds your email provider's file size limit. For example, the Gmail file size limit is 25MB. The app can also have a problem accessing your messages if you use two-step verification -- which is a security feature that requires two separate methods of identity verification -- to log in to your email account. To use the feature with Mail, check your email provider's documentation to get the specific procedure. For example, you need to create a separate App password for Mail before the app can access your Gmail two-step verification-enabled account.