Q: iPhone does not send email?

Try resetting your Mail Account. First close your Mail App completely from the app switcher window by double clicking the Home button and swiping up the Mail preview pane until it disappears from the screen. Then go to Settings > Mail, Contacts, Calendars > locate your email provider, click on the account and swipe to Delete. Then restart the device. Then go back to Settings > Mail… and add the account again.

Set up an email account on your iPhone, iPad, or iPod touch - Apple Support