It looks as if the "Contact Us" form for sending comments to the CentOS webmasters (http://www.centos.org/modules/contact/) is trying to send mail to donavan@mail.centos.org, which apparently gets forward to an account @4wx.net. The mail server for that domain is having a hard time communicating with mail.centos.org.
Is there anyone on this list who can confirm, deny, or report the problem? :-)