Site email problem

I have two sites, one is on Drupal and the other one is on Opigno. My drupal based site doesn't sent any emails to the users, no welcome, no sing up etc. But opigno based does it. I've changed several mailbox (my own site's mailbox, the public ones etc), result is the same - opigno based is ok, drupal based doesn't work. And that's very strange, because I've already had drupal based opigno lms several weeks ago with the same settings and it worked perfectly (unfortunately I've deleted that site). And I have installed SMTP module, and turned it on, stiil no result. I've already consulted with IT specialists and they don't understand what is the problem too. So you are my last hope!!