Warning: could not send message for past 4 hours

[Mail Delivery Subsystem]

**********************************************
    **      THIS IS A WARNING MESSAGE ONLY      **
    **  YOU DO NOT NEED TO RESEND YOUR MESSAGE  **
    **********************************************

The original message was received at Mon, 21 Nov 2011 23:20:34 +0800
from localhost.localdomain [127.0.0.1]

----- Transcript of session follows -----
451 fedoraproject.org: Name server timeout
451 fedoraproject.org: Name server timeout
451 fedoraproject.org: Name server timeout
Warning: message still undelivered after 4 hours
Will keep trying until message is 5 days old
451 fedoraproject.org: Name server timeout