As with most issues, there are a number of possible causes. The bounce back message will contain more detailed information on why this has happened. So if you acquired a copy of that email via an alternative route, it would help resolve the issue quickly. These are two of the most common reasons:
Insufficient Disk Space - If your email account has run out of disk space you will not be able to receive any emails until you have deleted some existing ones to free up space, or you have added more disk space.
MX Records - If your DNS isn't set up correctly, or more specifically your MX records, you may not be able to receive the emails being sent to you. MX records are responsible for all email delivery.
Please get in touch with our support team if you require further assistance.