Hello everyone!
How to enable/disable sending email to unregistered users when he/she submitting an ad?

What is it for and how does it work (look at the attach)?
I think something is working incorrect right here...

Not clear.

I modified questions, hope it's clearer now...

What is it for and how does it work (look at the attach)?
I think something is working incorrect right here...

Your attached screenshot for Alerts refers to User Subscription. When you got to the search page you will find an option to set alert for your search, so if any new item is posted in the category that you have set alert for, you will get an email notification saying new item is posted in your selected category.

Thanks, @Brandso. Still have to find the answer to the first question...

No simple answer to your first  question.

Is email sending enabled or disabled by default?

Of course enabled.

Can you tell me how to find the code to turn off the sending of the letter?

@Nick
It is somewhere in oc-includes/osclass/email.php I would say