If you don't need ALL your incoming mail, you can configure your mailbox to discard all incoming mail.
In this case senders won't receive 'undelivered mail' notifications.
1. Click the mailbox e-mail address in the E-mail list on the maildomain Controls page.
2. In the MAILBOX section check the Discard All Incoming Mail box.
3. Click the Submit button at the bottom of the form.