mass mailer prob

hi all i am new in here,now i use dolphin RC2 all success but in mass mailer if i sen tu all member sent success but all user not receive any massage from site and the massage sent back to site email error:- said send failed

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:


xxxxxxxxxxxx
    retry time not reached for any host after a long failure period

hello, maybe you site's members wrote wrong their email addres  ?

if wrong all user recieve registered members mail.

pls help me