2. Network Settings Disabled Email
Changed any of your settings lately? There are a few things that will disable your email functionality, so you'll want to make sure that you didn't accidentally change any of those settings.
If cellular data is turned off, Internet and email will not work on iPhone. To verify that cellular data is on, go to: Settings > General > Network. Cellular Data is the second option listed; it has a push button with On or Off as the only options. If it was off, turn it on and try sending your email again.
Turn off your Wi-Fi signal to force the phone to use cellular data to send your email. If a faulty Wi-Fi signal is being used, it can prevent your phone from sending messages. Sometimes the iPhone Wi-Fi signal shows as strong, but connectivity with the ISP is compromised for unknown reasons. Your phone will always use Wi-Fi when available if Wi-Fi is turned on, so disabling it will fix the problem if the Wi-Fi connection is the culprit.
When Airplane Mode is enacted on iPhone, all network connections are disconnected. No phone calls can be made and Internet and email are disabled. The option is a push button located at the top of the settings menu, so it is easy to turn on accidentally. If you see a small airplane symbol where your signal strength usually is, you've found the reason for your problems. Go to Settings and turn Airplane Mode to off.