Webmaster Email not reachable anymore?

Hi,

I tried 2 days ago, and again today, to send an email to webmaster@jazz.net, but mail delivery failed with following
returned mail:
-----------------------------------------------------------
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. The following addresses failed:

<webmaster@jazz.net>

domain name system error:
host spamguru009.watson.ibm.com:
mail exchanger not found
host spamguru010.watson.ibm.com:
mail exchanger not found
-------------------------------------------------------------

Last week it still had worked, so my question:
Does anyone else has this problem?