I guess that's a POP3 account.
The way POP3 works, it's not possible to access just message text separately from other stuff that may be there... and there isn't even a way to find out what's in a message without downloading its entire content.
With IMAP, the app only downloads message text and inline images, letting you pick attachments to include when forwarding (where you can select none at all, and they won't be downloaded).
PS - POP3 is from 1996, IMAP is from 2003. I remember the "smart phone" I had in 1996... it had no mail app