Remote SMTP Server Returned: 451 4.7.1

[xerex]

One of my users is having issues, everytime he send an email he gets this error. Is it my server or what?

From: Delivery Subsystem [mailtoOSTMASTER@xxxxx.com]
Sent: Thursday, December 01, 2005 7:30 AM
To: xxxx@xxxxxxxxx.com
Subject: Message Delivery Delay


Message is waiting at server01 for delivery to mail.xxxxx.com.

Message delivery has been delayed to the following recipients:
[SMTP:xxxx@xxxxxx.com]: Remote SMTP Server Returned: 451 4.7.1
Temporarily rejected. Try again later.

 

[Pavluha]

Check server01 mail server.
For example
nslookup mail.server01.com