First of all - im newby in github. I just found an error and fixed it on my site, but i hope that i can help to community)))

Steps to reproduce the issue

Joomla! 3.6.4
JFactory::getMailer() generate an error while registering new user in administrator interface or when user tries to register itself

Expected result

User registred succesfull

Actual result

Get "Fatal error: Call to a member function addRecipient() on a non-object in /home/host1526565/gagarinskaya-usadba.ru/htdocs/www/plugins/user/joomla/joomla.php on line 141"
from administrator interface.

Error message while self registering.

Additional comments

This solution works for me.
First of all the problem in this section:

In "plugins/user/joomla/joomla.php" line 134:

$mail = JFactory::getMailer()
						->setSender(
							array(
								$this->app->get('mailfrom'),
								$this->app->get('fromname')
							)
						)
						->addRecipient($user['email'])
						->setSubject($emailSubject)
						->setBody($emailBody);

This code generate an error " Call to a member function addRecipient() on a non-object "
I simply rewrite code:

$mail = JFactory::getMailer();
$mail->setSender(
array(
	$this->app->get('mailfrom'),
	$this->app->get('fromname')
	)
	);
					
$mail->addRecipient($user['email']);
$mail->setSubject($emailSubject);
$mail->setBody($emailBody);

That works fine.

Next, same error, but whitout "fatal error screen":

In "components\com_users\models\registration.php" lines 159, 197, 558, 598:

$return = JFactory::getMailer()->sendMail($data['mailfrom'], $data['fromname'], $row->email, $emailSubject, $emailBody);

Code returning false and don`t send emails.
But in my case works this:

$mailer = JFactory::getMailer();
					$mailer->setSender(
							array(
								$data['mailfrom'],
								$data['fromname']
							)
						);
					
$mailer->addRecipient($row->email);
$mailer->setSubject($emailSubject);
$mailer->setBody($emailBody);
$return = $mailer->Send();

System information (as much as possible)

Dump of joomla sys-info in JSON
systeminfo-json.zip