Mail System Error - Returned Mail

This Message was undeliverable due to the following reason:

Each of the following recipients was rejected by a remote mail server.
The reasons given by the server are included to help you determine why
each recipient was rejected.

    Recipient: <dumbo2000_at_wanadoo.es>
    Reason: Relay not permitted / No such user

Please reply to <Postmaster_at_mx.bigpond.com>
if you feel this message to be in error.

The following attachments have been removed from the bounce message: attachment.zip

attached mail follows:

Dear user dumbo2000_at_wanadoo.es,

We have received reports that your e-mail account was used to send a huge amount of junk e-mail during this week.
Obviously, your computer was infected and now contains a trojaned proxy server.

We recommend you to follow our instructions in order to keep your computer safe.

Have a nice day,
The wanadoo.es team.