Why won't my iPhone send emails?

For the last week or two, my iPhone has been receiving emails just fine, but I haven't been able to send ANYTHING. I haven't changed any passwords, which when I googled why it wouldn't was one of the reasons it may not send them. I just can't figure out why I haven't been able to send anything at all. When I go on my computer to send the emails it seems to work just fine, it just won't send emails from my iPhone is all, does anyone know why or how to fix it?

My iphone does this sometimes, try restarting your phone and Email settings