Theses parameters are used only if no smtp server are found in the database, code extract:

```python

mail_server = self.sudo().search([], order='sequence', limit=1)

if mail_server:

            smtp_server = mail_server.smtp_host

            smtp_user = mail_server.smtp_user

            smtp_password = mail_server.smtp_pass

            smtp_port = mail_server.smtp_port

            smtp_encryption = mail_server.smtp_encryption

            smtp_debug = smtp_debug or mail_server.smtp_debug

else:

            # we were passed an explicit smtp_server or nothing at all

            smtp_server = smtp_server or tools.config.get('smtp_server')

            smtp_port = tools.config.get('smtp_port', 25) if smtp_port is None else smtp_port

            smtp_user = smtp_user or tools.config.get('smtp_user')

            smtp_password = smtp_password or tools.config.get('smtp_password')

            if smtp_encryption is None and tools.config.get('smtp_ssl'):

```

So, in order to use the smtp values in the odoo.conf (or command line) the default mail server must be removed (or archived), then the system will use the provided arguments