Question : why does Exhg svr 5.5 not accepting e-mails from some domain?

We are running Exchange server 5.5, couple days ago, without any modification made to the Exchange server, for no reason, the server doesn't accept some of the domains e-mail at all.  it still sent mails without problem.  The only modification we had made to our network is to change the 2nd DNS from Network Solutions.  Any inputs will be appreciated...

Answer : why does Exhg svr 5.5 not accepting e-mails from some domain?

You may be able to get your ISP to disable their zone file. If thier DNS server stops responding to your requests, your DNS will take over right away. This will help to verify if the second DNS box is actually the problem.

MW