I can believe that; don't know enough to say either way.
However, when I first noticed it the space-used line said 7MB out of 7850MB (0%). When I changed it to only-forward, the entry got shifted out of the "mailboxes" section, and the "forwarded" section has no place for storage used, which makes sense But, when I shifted it back to not-forwarded to try POP/SMTP, it changed to say 7MB / 50MB (14%) available, which worries me.
If it is set up as you say, then my web space is now limited to only 50MB, which will cause trouble Real Soon Now.
I hope you're wrong.....