Sending email from your website with PHP mail() is possible on InfinityFree, but it is restricted. Only a small set of templates have been whitelisted, and any email which doesn’t match those templates will be dropped.
To work around this, you could send email with a third party SMTP service, like Gmail, instead. Alternatively, you could upgrade your account.
For more information, as well as general tips (Gmail SMTP) on how to ensure email from your website is sent successfully, please see this article: https://infinityfree.net/support/php-mail
Wordpress - some users successfully use the WP SMTP plugin (of course if you have wordpress)