503 Bad sequence of commands if count($this->all_recipients) == count($bad_rcpt)

[eddi13]

PHPMailer::smtpSend();
if all recipients is bad (count($this->all_recipients) == count($bad_rcpt)), then expected SMTP server reset or quit command, will nevertheless be sent DATA command.

If it wants to send a letter to multiple addresses in a loop, you beckommt after this failure, for each address, whether right or wrong, a rejection of the SMTP Server - 503 Bad sequence of commands, and no further emails of this loop be sent.
----------------------IMHO-------------------------
I have patched with me so:
rather than simply as

    if (!$this->smtp->data($header . $body)) {
        throw new phpmailerException($this->lang('data_not_accepted'), self::STOP_CRITICAL);
    }

yet to check the number that undeliverable addresses

    if (count($this->all_recipients) > count($bad_rcpt) && !$this->smtp->data($header . $body)) {
        throw new phpmailerException($this->lang('data_not_accepted'), self::STOP_CRITICAL);
    }

------------------------IMHO------------------------
The whole was tested at GMX SMTP with $this->SMTPKeepAlive == true and $this->SMTPKeepAlive == false