Question : 2 Exchange servers via same IMSS server

I have 2 mail servers xyz.com and ABC.com. My XYZ.com has a MX record but ABC.com doesn't have.
Now I want to create a MX record for ABC.com for receiving and sending mails to internet. Both are running MS-Exchange 2k3

Basically , my network diagram for exchange server XYZ.com is

XYZ.com ----> IMSS (Mail security server)-----> Internet
ABC.com------> NO Connection to Internet.

Now what i want is that my ABC.com exchange server should be deliver and receive the mails via the same IMSS server (connected to XYZ.com server).

Kindly help how can i do that so that same IMSS servers acts as spam filetring device for both the two diffrent domains...

Answer : 2 Exchange servers via same IMSS server

caution: I have only book knowledge on this setting, please verify and post back if it's working.

- register a new MX record for abc.com, pointing to IMSS
- on Exchange server that is responsible for xyz.com, create a new receipient policy that hands out email addresss @abc.com, you can make the filter in a way so that it won't actually stamp any user in that domain. CLEAR the option that "this Exchange org is authorative for this domain"
- for receiving emails sent to abc.com, configure the smtp virtual server on [email protected] as follows:
 in ESM, go to:
Servers/Your_Server/Protocols/SMTP/Your_SMTP_Virtual_Server
Right-click Your_SMTP_Virtual_Server, and then click Properties. mail tab "send all un-resolved email to"

- for delivery abc.com email to internet, use smart host on [email protected]:
 in ESM, go to:
Servers/Your_Server/Protocols/SMTP/Your_SMTP_Virtual_Server
Right-click Your_SMTP_Virtual_Server, and then click Properties. deliver tab, advanced, smart host