[Exim] 503 Error

I have been googling around trying to find out why an email is hanging
around in my queue, it keeps getting 503 errors

2003-11-05 12:15:15 1AHMYr-0003H1-1q ** <snip>@263.net R=dnslookup
T=remote_smtp: SMTP error from remote mailer after RCPT
TO:<<snip>@263.net>: host mx09.263.net [211.150.96.29]: 503 Error: need
MAIL command

Any clues ?

Ron

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Ron McKeating
Senior IT Services Specialist
Internet Services and Software Solutions
Loughborough University
01509 222329