Dong CHE has told me that mail from mail.freebsdchina.org has been bounced back because it was listed in rblplus.mail-abuse.org. From the query page I found mail.freebsdchina.org were listed in mail-abuse.org’s DUL by mistake (I believe so because the mail.freebsdchina.org block is not owned by dial up user).

After I have contacted them they have removed our network block from DUL. This permits us to send mail to the world again.