when i send email below address i got this message.(several time)

1)Delivery to the following recipient failed permanently:

 northstate@bigpond.com

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain bigpond.com by extmail.bigpond.com. [61.9.189.122].

The error that the other server returned was:
550 5.1.1 <northstate@bigpond.com> recipient rejected. IB603a

2)Delivery Status Notification (Failure)
The following message to <andrew@aztecblades.com> was undeliverable.
The reason for the problem:
5.1.0 - Unknown address error 550-'sorry, no mailbox here by that name (#5.1.1)'

3)Mail delivery failed: returning message to sender
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. This is a permanent error. The following address
failed:

"northstatetownsville@bigpond.com":
SMTP error from remote server after RCPT command:
host: extmail.bigpond.com
5.1.1 <northstatetownsville@bigpond.com> recipient rejected. IB603a

can anyone help me how to solve this.

It says andrew@aztecblades.com doesn't exists, send to the right address.

Yep - right here:
The following message to <andrew@aztecblades.com> was undeliverable.
The reason for the problem:
5.1.0 - Unknown address error 550-'sorry, no mailbox here by that name (#5.1.1)'