WordPress at a glance
function is not described

PHPMailer\PHPMailer

PHPMailer::isMail() public WP 1.0

Send messages using PHP's mail() function.

{} It's a method of the class: PHPMailer{}

No Hooks.

Return

null. Nothing.

Usage

$PHPMailer = new PHPMailer();
$PHPMailer->isMail();

Code of PHPMailer::isMail() WP 5.7.2

<?php
public function isMail()
{
    $this->Mailer = 'mail';
}