Override mailSend for older version of WordPress

[rajumsys]

While investing this issue, I've found that phpMailer invokes sending method differently in older version. phpMailer with wordpress 4.4, invokes "{$this->Mailer}Send".

WordPress 4.4.2

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);
            }

WordPress 4.2.2

switch ($this->Mailer) {
                case 'sendmail':
                    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:
                    return $this->mailSend($this->MIMEHeader, $this->MIMEBody);
            }

Specially, notice these two lines differences:
4.4x

default:
   $sendMethod = $this->Mailer.'Send';
    if (method_exists($this, $sendMethod)) {
        return $this->$sendMethod($this->MIMEHeader, $this->MIMEBody);
    }

    return $this->mailSend($this->MIMEHeader, $this->MIMEBody);

4.2x

default:
    return $this->mailSend($this->MIMEHeader, $this->MIMEBody);

We can probably simply override mailSend in addition to custom mailer which should satisfy both version.

[rajumsys]

This has been fixed in v2.2.1