Default Outgoing SMTP Server using site_config.json not working

I am using following configuration for the the erpnext instance for setting default outgoing SMTP Server programmatically . But it doesn’t work.
“db_name”: “f2bc298b7c”,
“db_password”: “x5oWvYP6PieoviA2”,

“mailserver”: “”,
“mailport”: 587,
“usessl”: 1,
“maillogin”: “”,
“mailpassword”: “password”,
“autoemailid”: “”,
“emailsendername”: “Notifications”,
“alwaysuseaccountemailidas_sender”: 0

Can you share an error trace?

There is no error trace , following is the configuration I am using in the site_config.json
"mailserver": "", "mailport": 587, "usessl": 1, "maillogin": "", "mailpassword": "password", "autoemailid": "", "emailsendername": "Notifications", "alwaysuseaccountemailidas_sender": 0 }

Everything works fine except no default SMTP server is configured .