Exchange 2k3 Mail Sending Not Receiving

Recently in our company we deployed the exchange server 2003.Already in that server the domain was configured.Now we created the the mailbox for all the users in our company.Now the problem is users can able to send the mail to the other user but the destination user cannot able to received that mail,this problem is happening to all the users in our company.The mails are sending but not reciving.If anyone help me out of this issue.