Cannot receive registration e-mails

I am trying to resolve this with host company.

As the emails are leaving CB fine there's nothing more I can advise unfortunately. Once they've reviewed their logs they should be able to see why the emails were rejected. You may also want to try using Google SMTP mail server if you've a gmail account and see if it works.

I read somewhere that someone solved a non-receiving e-mails problem, after he saw that in phpmyadmin db the sendmail value of new users had default value 0. He changed it to 1 and could receive mails. I did this also, but when i try to register new user, then i receive no e-mails and if i see thew new db record the sendmail value is 0, instead of 1 that i have put at default structure value.

You've just set all your users to receive moderator emails. Please reverse your change. Only moderators should have that parameter set to 1.

Ok, i will try to resolve this with my hosting company.

One last question... Is there a possibility of being hacked?Because one of the representatives of hosting company told me that he saw the registration mails produced but being queued and not sent.

One last question... Is there a possibility of being hacked?Because one of the representatives of hosting company told me that he saw the registration mails produced but being queued and not sent.

I doubt it. The emails are being placed in the mail server queue which is completely independent of your domain and your website. The queue is then exited and not processed. My guess is a configuration issue perhaps on the mail server.

The best I can suggest is to try using Google SMTP with a gmail account and see if the emails send fine. If they do then it's absolutely not your site. If you choose to do this please see the below regarding proper configuration of Joomla mailer settings for Google SMTP.

Mailer: SMTP Server
SMTP Authentication: Yes
SMTP Security: SSL
SMTP Port: 465
SMTP Username: Your Google Username
SMTP Password: Your Google Password
SMTP Host: smtp.gmail.com

Note you may need to append the port to the host as follows.

SMTP Host: smtp.gmail.com:465