My Heberger ( Provider ) blocks PHPMailer for security reasons.
That's why I need to use the SMTP server on the site.
How to activate by default SMTP OSSN ??
Here is the ONETSOLUTIONS.NET admin response
In the context of securing outgoing emails, it is preferable not to use the MAIL PHP function, which is why we have removed it. MAIL PHP does not require any authentication, so this is an open door to some malicious scripts.
We recommend that you use SMTP, a protocol that requires authentication.