We are running Windows NT 4.0 OS in an Exchange Server 5.5 environment. We have a mailbox with a SMTP address that has been set up with a different domain (site address). We added the MX record in DNS and also, selected: Internet Mail Connector > ROUTING TAB and added the domain name and checked "REROUTING INCOMING SMTP MAIL". In the SENT TO field, we added the domain name and in the ROUTE TO field, we put INBOUND. So, on the email side, we have the Exchange mailbox in place with the appropriate SMTP email address, the MX record has been added in DNS, and in the INTERNET MAIL CONNECTOR, that domain name has been added so it will reroute INBOUND. When mail is send from external to this mailbox, it responds back to the sender with the following error message: xxx.xxx.xxx.xxx does not like recipient. Remote host said: 554 mailbox unavailable. Giving up on xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx is the IP Address) Does anyone know what could be causing this type of error message? Is this a firewall issue? I don't see anything on the mail side. Thanks, Kenneth Kwong --------------------------------- Do You Yahoo!? Try FREE Yahoo! Mail - the world's greatest free email!