Returnd mail Canot send mesage in 5 days

In my whole company everyone is using email without a problem. One user tryes to send email to China and gets the following error message:
” Returned mail: Cannot send message within 5 days
FROM: Mail Delivery Subsystem
RE: Returned mail: Cannot send message within 5 days
—– The following addresses had permanent fatal errors —–
Deferred: Name server: simple-elec.com: host name lookup failure
Message could not be delivered for 5 days
Message will be deleted from queue “