The mail server, by default, accepts mail, processes it, and when it finds out that there is no such a recipient under the domain, it returns the mail back to sender with an error message.
You can choose to modify the default settings so that the mail server will:
- Continue returning all such mail back to senders (Bounce with message option),
- Forward all such mail to the specified email address (Forward to address option),
- Forward all such mail to another mail server with the specified IP address using the option Redirect to external mail server with IP address (available only for Windows hosting), or
- Reject such mail without accepting it and without notifying senders (Reject option).