I think he's asking how to make ftpd chattier about over-quota situations.
@RattleSn@ke: I don't know off the top of my head, and I don't have time right now to set up a test scenario for tinkering.

My suggestion would be to give the
ftp/vsftpd port a try to see if it's providing better "quota feedback". That may or may not be addressing the root cause...