Delivery Delay notification

When forwarding to a exteral mail account , and then
, I firstly receive a Delivery Delay notification, then a undeliverable message:
“Could not deliver the message in the time limit specified. Please retry or contact your administrator.”
i can send new email without problems.
I’m running Exchange 2000 with SP3 on Windows 2000 advance server SP3.
there is another server fro connecting to the internet

When sending to those specific accounts via hotmail, the mail is sent.