451 please retry later (gl)

Hi,

I have multiple Mailbox servers. All servers are working fine. Except one mailbox server. Whenever this mailbox server send any email, it stucks in the queue and gave the following error.

451 please retry later (gl)

users get delivery delayed message. Whereas other mailbox servers send emails to the same domain. It is very strange that one mailbox server cannot send any email to any domain. Can somebody please help us in this regard.

Thanks

Anees