Emails are not sent
If you are not receiving some email notifications please make sure that in wp-admin Email Templates edition panel “Enable this email notification.” checkbox is checked for the email template that is not being sent.
Job board email templates might be sometimes confusing so also be sure to check Email Templates category In KB to find out when and to which email address the emails are sent (maybe you are checking wrong email account?).
When sending emails it is sometimes hard to determine if the email was not sent or not delivered, to make sure that WordPress is actually sending emails you can use Email Log plugin. It will log every email sent by WordPress, if one of the emails is there but not in your inbox then this is a problem with your email delivery and you should try to setup SMTP email delivery.
Sending Emails via SMTP
If some or all of your emails are sent but not delivered to your inbox, it might be a problem with your server sendmail. The best thing you can do at this point is to setup SMTP email delivery which is much reliable when it comes to email delivery but harder to setup.
There are multiple SMTP plugins in WordPress plugin repository, you can find them here: http://wordpress.org/extend/plugins/search.php?q=smtp, however the one i tested and can recommend is WP Mail SMTP.