PHPMailer\PHPMailer

PHPMailer::addCustomHeader │ public │ WP 1.0

Add a custom header. $name value can be overloaded to contain both header name and value (name:value).

Method of the class: PHPMailer{}

No Hooks.

Returns

true|false. True if a header was set successfully

Usage

$PHPMailer = new PHPMailer();
$PHPMailer->addCustomHeader( $name, $value );
$name(string) (required)
Custom header name.
$value(string|null)
Header value.
Default: null

PHPMailer::addCustomHeader() code WP 7.0

wp-includes/PHPMailer/PHPMailer.php 
public function addCustomHeader($name, $value = null)
{
    if (null === $value && strpos($name, ':') !== false) {
        //Value passed in as name:value
        list($name, $value) = explode(':', $name, 2);
    }
    $name = trim($name);
    $value = (null === $value) ? '' : trim($value);
    //Ensure name is not empty, and that neither name nor value contain line breaks
    if (empty($name) || strpbrk($name . $value, "\r\n") !== false) {
        if ($this->exceptions) {
            throw new Exception(self::lang('invalid_header'));
        }

        return false;
    }
    $this->CustomHeader[] = [$name, $value];

    return true;
}