Retrieves related parts if the message is a multipart/related message, returns FALSE if there are no related parts.
The optional $secureMIME argument allows the types of files allowed in a multipart/related message to be limited. This feature can be used to prevent the browser from automatically downloading potentially malicious files embedded in a message.
| param | int | &$mid message id |
| param | str | &$pid part id. |
| param | bool | $secureMIME (optional) See above. |
| return | array|FALSE | |
| throws | ErrorStack: Message structure does not exist. | The method was unable to find the message structure associated with the message id passed. |
| access | public | |