This error message is not a SelectHR error, and is instead produced by the Mail Server (often you will see the From of the email reference Mailer-Daemon).
When you get a [email protected] message in your inbox, the server at that company is informing you that it is returning your message because of some failure.
Some common causes are:
The email address does not exist
The email address is invalid
The email address has a spelling mistake
The domain does not exist
There is a routing issue
These issues are not related to SelectHR and are produced by the Mail Server itself. As such, if you encounter this issue, check that the common causes outlined above are not the cause and refer to your IT Team for further assistance.