Undelivered Mail Returned to Sender

This is the Postfix program at host physsmtp.wustl.edu.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to <postmaster>

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                        The Postfix program

<ruoff_at_howdy.wustl.edu>: host wuphys.wustl.edu[128.252.125.70] said: 550 5.1.1
    <ruoff_at_howdy.wustl.edu>... User unknown (in reply to RCPT TO command)

attached mail follows:

The message was undeliverable due to the following reason:

Your message was not delivered because the destination server was
not reachable within the allowed queue period. The amount of time
a message is queued before it is returned depends on local configura-
tion parameters.

Most likely there is a network problem that prevented delivery, but
it is also possible that the computer is turned off, or does not
have a mail system running right now.

Your message was not delivered within 7 days:
Mail server 59.54.82.220 is not responding.

The following recipients could not receive this message:
<ruoff_at_howdy.wustl.edu>

Please reply to postmaster_at_howdy.wustl.edu
if you feel this message to be in error.