Display error if mail function not working?

I'm building an Email verification script and i'm using ajax so whenever the user fill in a false or an invalid email, an error bar with the error name will be displayed, And when the email is true and belongs to an active account, an email will be sent to the user with instructions and the error bar says email sent. The problem is even the mail function isn't working, the error bar keeps saying email sent. So i wan't some lines to detect if the email wasn't sent to show "email was not sent" in the error bar.