During each analysis, the notifications are computed for each user who has subscribed to notifications. Then, in an asynchronous way, these notifications are sent to users by emails.
To set the delay between processing of notification queue, set the
sonar.notifications.delay property (in seconds) in SONAR_HOME/conf/sonar.properties. Note that the server has to be restarted for the new value to be taken into account.
To configure the email server, go to Settings > General Settings > General > Email.
Check also the Server base URL property at Settings > General Settings > General > General to make sure that links in those notification emails will redirect to the right SonarQube server URL.