Steps to reproduce the issue

In Global Configuration, set the New User Account Activation
to None
Then try to register a new user.

Expected result

The user is created with no errors or warnings

Actual result

The user is created with the following errors/warnings
Warning :
Message
The mail function has been disabled by an administrator.

Error :
An error was encountered while sending the registration email. A message has been sent to the administrator of this site.

System information (as much as possible)

apache 2.4.18-2ubuntu3.9
Joomla 3.8.13

Additional comments

I am in a localhost and do not have mail setup. So I understand why I get those errors.
The problem is that I am developing a component and in my controller I call the register() method
of the UsersModelRegistration.
Because there is no mail in my system the method returns false which is not true because the user is created.
The point is that since the New User Account Activation is set to None and the user is created then the returned value from the UsersModelRegistration::register method should return true (even with warnings) because the requested action (user registration) is completed.

In the UsersModelRegistration :

	public function register($temp)
	{
		$params = JComponentHelper::getParams('com_users');
    JLog::add('$params :' . print_r($params,1), JLog::DEBUG, 'site.user.registration.model.register');
...

The log

 DEBUG 127.0.0.1 site.user.registration.model.register   $params :Joomla\Registry\Registry Object
(
    [data:protected] => stdClass Object
        (
            [allowUserRegistration] => 1
            [new_usertype] => 2
            [guest_usergroup] => 9
            [sendpassword] => 0
            [useractivation] => 0
            [mail_to_admin] => 0
            [captcha] => 
            [frontend_userparams] => 1
            [site_language] => 0
            [change_login_name] => 0
            [reset_count] => 10
            [reset_time] => 1
            [minimum_length] => 4
            [minimum_integers] => 0
            [minimum_symbols] => 0
            [minimum_uppercase] => 0
            [save_history] => 1
            [history_limit] => 5
            [mailSubjectPrefix] => 
            [mailBodySuffix] => 
            [debugUsers] => 1
            [debugGroups] => 1
            [sef_advanced] => 0
            [custom_fields_enable] => 1
        )

    [initialized:protected] => 1
    [separator] => .
)