“Sending’ reported error (0x800CCC65) : ‘Your outgoing (SMTP) e-mail server has reported an internal error. If you continue to receive this message, contact your server administrator or Internet service provider (ISP). The server responded: 503 Valid RCPT command must precede DATA’”
The reason for this issue is that your mail client fails to authenticate to the server. Generally, this is caused by the MS Outlook SMTP authentication is not switched on.
Another possible reason for the issue is an Antivirus or Firewall software which is checking your outgoing mail connections. In case you have set properly your mail client as explained above and the issue persists, turn off the antivirus and the firewall software you have installed on your local computer and try sending out e-mails again.