You probably need to change the configuration under Admin > Email Settings
or maybe you can't connect to your email server (connection down, blocked by firewall, etc.).
Look at the record for the notification, which is found in the APP_MESSAGE table in the database to make sure that it is sending to a valid email address and coming from a valid account.
Remember that the email's FROM line should be the same as the email account that you configured under Admin > Email Settings
. For example, if you configured to send email from the account of [email protected]
, but you are trying to send it from the account of [email protected]
, then most email servers will reject the email as spam.