PSE 12: When re-sizing large format photos, why does PSE 12 compress them?

Hello, I have elements 12 and it seems that when I resize a large format photo to example 4M it appears as K in the information box.  Why is it being compressed?  I have to have accurate M to send to juried shows and it seems that when I sent a 300 dpi 6M for print via e-mail the recipient got the image at 424K.  What am I doing wrong or is it the program?  Thanks  Bill