Hidden message

I just tried to send an e-mail to my mom...here's the message I got in return:

Hi. This is the qmail-send program at
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

:
68.168.78.104 does not like recipient.

Hmmmm...I wonder if I should be worried?!