A bounced back message can be received for a variety of reasons. If the sender’s e-mail address or IP have been blacklisted by global anti-spam organizations, he should receive this information and instructions on how to proceed along with the bounced e-mail. If this is not the case, please make sure that:
- Your MX records are correct
- You have not exceeded your e-mail quota (if there is one for your e-mail account). The quota can easily be reviewed from your cPanel->Email Accounts – it should be represented by a bar, located next to each address on your hosting account.