SMTP
504 Parameter Not Implemented
A command parameter is not implemented on this server. The command itself is valid but the specific parameter or extension you used is not supported.
Когда вы видите этот код
When using SMTP extensions or parameters that the server does not support, such as an unsupported AUTH mechanism or an unrecognized MAIL FROM parameter.
Как исправить
Check the server's EHLO response for supported extensions and parameters. Use only the mechanisms and parameters listed in the server's capability advertisement.