How can I prevent the Mac OS 'Mail' app from reducing the file size of image attachments?

If I am entering a photo in a competition, I want to send it with the highest file size allowable. Many competitions require entries be jpg files, less than some specific file size. For example, say that limit is 10 MB. If I convert a 455 MB image to jpg, a quality setting of 11 will give me a file size of 8.4 MB.

If I send that 8.4 MB image using the Mac OS 'Mail' app, the image is further compressed to 542 KB. If I send it by Gmail, using a browser like Safari, it is sent as is, arriving with a file size of 8.4 MB. The difference in image quality is dramatic.

Is there any way to force Mail to send the file without additional compression?