Message Delayed Msgs....

Hi,

I have an issue with a particular domain that doesn't seem
to be  
happening to anyone else except this one domain, where
senders are  
getting "msg delayed" msgs sent back to them.

My silly questions are:

a.) where do I turn off that warning ?

and more importantly b.) what the hell is going on and how
the hell  
do I fix it ?

M i l e s.