From what I can find on the Internet, this is a "friendly-fied" version of email server error number 5.7.1 . It indicates that recipient server has rejected a message because the sending server is misconfigured. An AI summary of the situation is... "The SMTP 550 5.7.1 error indicates that the recipient's server rejected your email due to security, policy, or authentication issues, such as a blocked IP, missing DNS records (SPF/DKIM), or missing SMTP authentication. The most effective immediate fixes are ensuring "SMTP Authentication" is enabled in your email client settings and verifying that your email domain is properly authenticated." Google "email error 5.7.1" for more info., I believe that you the user cannot directly do anything about it except to report it to your email administrator. The only thing you can do on your end that might help is confirm that your SMTP server settings indicate the proper Authentication Method,