SMTP
500 Syntax Error
The server could not recognize the command due to a syntax error. The command line was malformed or the command is not recognized by this server.
When You See This Code
When you send a command the server does not understand — often due to a typo, unsupported command, or an excessively long line.
How to Fix
Check the command spelling and syntax against the SMTP specification. Ensure the command line does not exceed 512 characters and uses proper CRLF line endings.