STEEMIT registration ( ERROR : mail: to <********>, from <null>, template confirm_email (not sent due to not production env)

I have installed site steemit and mining on my own server.

When I running the site steemit on Ubuntu 16 , its starts ok, .

and when I trying to registering a new user, in the www.my-steemit-site.com , I will not receive the confirmation in my email box.

In the console I see the logs:

mail: to user@email, from null, template confirm_email (not sent due to not production env)

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How I can I add the production env and what is the value of this?