[fetchmail] non-ascii email box id

I had a little problem with fetchmail which failed to accept messages
sent from people with non-ASCII characters in the MAIL FROM. In fact, is
it a sendmail or fetchmail problem?

How should I set my /etc/fetchmail.rc to accept those messaegs?

here is the log entry. the "????" were actually 8-bit characters that
made up a Chinese name (big5/GB character encoding).

Dec 22 00:30:05 server fetchmail[3481]: SMTP error: 501 5.1.7 Syntax
error in mailbox address "????**(_at_)china(_dot_)com" (non-printable character)

Dec 22 00:30:05 server fetchmail[3481]: mail from
FETCHMAIL-DAEMON(_at_)server(_dot_)myhome(_dot_)org bounced to postmaster