wp-includes/PHPMailer/PHPMailer.php:1842Actually send a message via the selected mechanism.
bool public function postSend() { try { //Choose the mailer and send through it switch ($this->Mailer) { case 'sendmail': case 'qmail': return $this->sendmailSend($this->MIMEHeader, $this->MIMEBody); case 'smtp': return $this->smtpSend($this->MIMEHeader, $this->MIMEBody); case 'mail': return $this->mailSend($this->MIMEHeader, $this->MIMEBody); default: $sendMethod = $this->Mailer . 'Send'; if (method_exists($this, $sendMethod)) { return $this->{$sendMethod}($this->MIMEHeader, $this->MIMEBody); } return $this->mailSend($this->MIMEHeader, $this->MIMEBody); } } catch (Exception $exc) { $this->setError($exc->getMessage()); $this->edebug($exc->getMessage()); if ($this->Mailer === 'smtp' && $this->SMTPKeepAlive == true && $this->smtp->connected()) { $this->smtp->reset(); } if ($this->exceptions) { throw $exc; } } return false; }Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/PHPMailer/PHPMailer.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.