If you have changed your DNS settings, and these were faulty (eg removal of the MX record for your domain), it will take 24 to 48 hours after resetting the DNS settings to restore the correct functionality. This is among the TTL in the DNS zone that is usually set to 24 hours.
Please proceed as follows:
1) Put your DNS settings back to "default" in the customer panel.
2) Wait 48 hours.
3) Test the email functionality again from an email address of another (external) provider.
If still errors occur, please contact directly the support, quoting the relevant email address. Attach a meaningful error message (such as mail delivery error)to your e-mail.