You must setup your software to properly send emails through your host. Setting up this feature can be frustrating for some particular hosts. Some configurations may work for a specific email or set of emails or recipients or may just work for a specific period until your host changes their STMP configuration. As such we can only supply general suggestions to try instead of specific things that will work. Ultimately how this feature is configured is up to your host.
E-MAIL SETUP > GENERAL E-MAIL SETTINGS