Emailing full resolution photos

I would like to email full resolution photos. When I email them from within Photos and hit Send and get several choices from Small to Actual Size. Actual size should be correct right? But when the email reaches the other end, the files seems smaller. For example, I have one photo that says Actual Size is 3.8 mb, but the file in the email ends up about 2 mb.

Am I missing something?