Select the "Forward original message as attachment" checkbox, if you want the original email to be attached to your message. Otherwise it will be included into your message body. Click on the "Send" button.
A confirmation message will appear on your display.
When you forward the original message as attachment, its original formatting and images in the body are kept. Whereas when you append the original message to message body, the message is converted into plain text, images in the body are remove and its attachments are attached to the message.