WordPress at a glance
function is not described

PHPMailer\PHPMailer

PHPMailer::getSentMIMEMessage() public WP 1.0

Returns the whole MIME message. Includes complete headers and body. Only valid post preSend().

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

No Hooks.

Return

String.

Usage

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

Notes

Code of PHPMailer::getSentMIMEMessage() WP 5.7.2

<?php
public function getSentMIMEMessage()
{
    return static::stripTrailingWSP($this->MIMEHeader . $this->mailHeader) .
        static::$LE . static::$LE . $this->MIMEBody;
}