I don´t get  any kind of mails. I get this message:

The system wasn't able to send the email to the specified address, if the problem persist please contact the administrator.

I have changed Admin Area>Configuration>login/registration option and define my mailsender.

Is it possible that my hots provider have disabled mail () function? 



 

I had a similar problem.  Check to make sure that your SMTP setting in PHP are pointing to the correct SMTP server.  Also check with your mail server that it can accept mail from your installation.  That was my problem.  As soon as the mail server was set to accept mail from my docebo server, it worked just fine.