509 Bandwidth Limit Exceeded
Meaning
A non-standard status code indicating that the bandwidth usage limit has been exceeded. Often used by hosting providers when a site goes over its allotted bandwidth.
When to Use
When a server or site has a bandwidth quota and that quota is exceeded, some servers (especially in shared hosting environments or control panels like cPanel) use this code to signify that no further data can be served until limits are reset.
Example
If a website has a monthly bandwidth cap and it is reached, requests to the site might start returning 509 Bandwidth Limit Exceeded, often accompanied by a page explaining that the bandwidth limit has been reached.
When Not to Use
Do not use in standardized HTTP contexts, since 509 is not an official code. This is specific to certain server setups. For general use, a 503 Service Unavailable might be used to indicate resource limits, but many stick to 509 for bandwidth issues for clarity in hosting environments.
Source
Unofficial (Apache/cPanel)