If iPhone is unable to receive email, try the following:
If you’re using one or more computers to check the same email account, that may be creating a lock-out issue. For more information, go to www.apple.com/support and search for TS2621.
Set up your email account directly on iPhone instead of syncing it from iTunes. In Settings, choose “Mail, Contacts, Calendars,” tap Add Account and enter your account information. If iPhone is unable to locate your service provider’s settings when you enter your email address, go to www.apple.com/support and search for HT1277 to get additional help in setting up your account.
Turn iPhone off, then turn it on again. Press and hold the Sleep/Wake button on top of iPhone for a few seconds until a red slider appears, and then drag the slider. Then press and hold the Sleep/Wake button until the Apple logo appears.
Turn off Wi-Fi so iPhone is connecting to the Internet via the cellular data network. In Settings, choose Wi-Fi and turn off Wi-Fi.
For additional troubleshooting information, go to www.apple.com/support and search for TS1426. If you still can’t receive email, you can call an Apple Expert (not available in all countries). Go to www.apple.com/support/expert for information. If Apple Expert is not available in your country, get a free GMail, Yahoo!, or AOL account and try forwarding your mail to that account.