Generic protocol error (SMTP error). The remote SMTP response to our EHLO with a 500 level error and the sending system will ...

{4}: Generic protocol error (SMTP error). The remote SMTP response to our EHLO with a 500 level error and the sending system will QUIT the connection and report this with non-delivery report indicating the remote SMTP server cannot handle the protocol. (For example, if an Outlook.com account is no longer active, a 550 SMTP error will occur.) Troubleshooting: Run an SMTP protocol log or a Network Monitor trace to see why the remote SMTP server rejects the protocol request.