Send mail in cron job meteor

I want to schedule email function to run at once in a day, But it showing me an error -"( Mail not sent; to enable sending, set the MAIL_URL environment variable. )", This message is showing only in cron job email function. New registered users are getting emails successfully. Can anyone please help me here why is this happening. Thanks in advance.

The error message seems pretty straightforward. How are you running your job? Where?