Give something for free, and the bad actors will come and abuse it in their droves!
Due to spam abuse the ability to send email on free hosting is highly restricted, and offered on a 'best effort' basis.
PHP sendmail is enabled on a really limited basis on free hosting where only registration signup emails from forums are delivered and similar types of message. You can not use PHP sendmail on free hosting for sending any emails other than registration emails from popular scripts such as forums and blogs.
You can use a remote SMTP server on free hosting such as Google for domains or Microsoft Live domains email account.
If mail() or smtp support is required please upgrade your account, a full list of features on our premium hosting can be seen here :
To upgrade to premium click the UPGRADE ACCOUNT button in your free hosting cPanel, using this method to upgrades all your existing files/domains/databases to premium hosting automatically.
Another option for reliable email sending on free hosting is to use Mandrill.com, a free account with mandrill allowed 12,000 emails per month. And the following plugins can be used for common scripts to integrate.
Joomla : https://connect.mailchimp.com/how-to/38
Wordpress : https://wordpress.org/plugins/wpmandrill/
If your application does not have a mandrill plugin and DOES support using SMTP you can configure your application to use mandrill over SMTP
https://mandrill.zendesk.com/hc/en-us/categories/200277207-SMTP-Integration give advice on the settings.