The following is dreamhost support replied me:
On Tue, 27 Sep 2011, you wrote:
All my emails to qq.com mailbox got following error, pls help!
This is the mail system at host homiemail-a72.g.dreamhost.com.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
If you are a current customer of DreamHost, please contact our
technical support team here
If you are not a customer please use our contact form at.
If you do so, please include this email in your support ticket. You can
delete your own text from the attached returned message.
Dreamhost Email Support
email@example.com: host mx3.qq.com[220.127.116.11] said: 550 Ip frequency
reply to RCPT TO command)
Thank you for contacting technical support. It looks like the the
nameservers are pointing to qq.com and the mx records are as well. I went
ahead and searhed our system for the mailbox firstname.lastname@example.org, but it
does not exist on our system. You will need to contact the company that
you have your email hosted at it to get your email working again.
Thanks and I do apologize for the issues you are experiencing.