I can receive emails but I can’t send them. Any fixes?

See this for help.

If you can’t send email on your iPhone, iPad, or iPod touch - Apple Support

Not sure if this step is in the linked article or not, but sometimes a forced reboot can help, and other times go into the settings, remove that email then add it back. Sometimes an iOS update will mess up the settings and the easiest way to fix it is to just add the email all over again.