Returned mail: User unknown

The original message was received at 2009-08-11 23:05:17 -0700
from postoffice.cc.shawcable.net [10.0.0.1]

----- The following addresses had permanent fatal errors -----
<ursulamedley@shaw.ca>

-----Transcript of session follows -----
... while talking to postoffice.cc.shawcable.net.:
>>> RCPT To:<ursulamedley@shaw.ca>
<<< 550 5.1.1 unknown or illegal alias: ursulamedley@shaw.ca
550 <ursulamedley@shaw.ca>... User unknown