And only when it says Actual Size will the file be right. If it's set on small, medium or large files size will be reduced and will be turned into jpegs, no matter what the original version was.
So open up an email and attach a file and look at what it says. If it says anything but Actual size the file is already altered. So change it to actual size and save as draft, which you can then delete.
Then next time you attach an image it should say Actual Size because it defaults to whatever was last used. If it still changes then the file is probably too big, most emails have size limits and it's different for every service, so you have to check not only your own but the receiver of the email because if it's past their limit they will never get it.