A bounce back email is dependent on the sender and receivers email address. If the receivers email address is incorrect, a bounce back email is generated to the senders email address.

In the case of Web TimeSheet instances hosted by Replicon, the sender's email address for Welcome Emails and System\Warning mails are hard coded and do not support bounce back email. Hence, when a user is added to Web TimeSheet with an invalid email address, the system triggers a welcome email. However as the recipient's email address is invalid a bounce back email gets triggered. As the senders email address does not support bounce back email, the same do not get recorded.

Hence, in Replicon there are no bounce back emails recorded for Welcome Email and System\Warning emails that fail to reach their destination.