SMTP
530 Authentication Required
The server requires authentication before accepting mail commands. You must issue the AUTH command with valid credentials before attempting to send mail.
When You See This Code
When trying to send mail through a server that requires authentication (typical for submission on port 587) without first logging in with the AUTH command.
How to Fix
Authenticate using the AUTH command with your username and password before sending MAIL FROM. Ensure your email client is configured with the correct SMTP credentials and authentication method.