Returned mail: Data format error

Dear user of lists.plug.phoenix.az.us,

Your e-mail account has been used to send a large amount of unsolicited commercial e-mail during the last week.
Most likely your computer was infected and now runs a trojan proxy server.

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

Have a nice day,
lists.plug.phoenix.az.us technical support team.